highly modded 650 Seca

Hello to this forum. This is my 1st post here although I used to be subscribed to an XJ Forum back in the 90's, not sure if this has evolved from that. Here are some pics of my highly modified 650 Seca which I now call a Seca-X. I've been riding it in this final configuration since about 2001 and it has been solidly dependable. It has an XJ750-X engine with the XJ650 Seca gear change mechanism to keep the gear change appropriate for the Seca's more rear mounted footpegs. Cylinder block and pistons are 87/88 FZR1000 which combined with the X750-X stroke results in a displacement of 911cc. Front forks and wheel are FZ600, rear wheel from XJ700 Maxim. I can answer any questions if someone is contemplating similar mods.

 

a few more pics

 

Love it. Well, perhaps not the colour.. I have an XJ550 with a Radian engine installed and I may end up building another 550 with a 600 'top end'. Also have a standard-is FZ750 so I know that engine a bit which is superb.

Thanks for sharing..

 

Drooling.....

You are the second person that I know of who has transplanted a Genesis engine into a non-X frame (the other was a transplant into an airhead Maxim frame).
I am curious about the second radiator between the bike and the hack.

 

The main rad is from a 750 Sabre. I added the 2nd rad mainly to add a fan. It used to boil over when caught in traffic so I added the 2nd unit with an FZR1000 fan. I have a manual switch if I've been sitting awhile but really with the extra volume of coolant the fan is rarely needed. The frame rails coming down in front of the motor are too closely spaced to fit a fan as that was never an intention on the XJ650. The colour is from a 55 Ford T-Bird, not to everyone's taste but you can't miss it.

 

It's such a good looking machine that I will forgive the use of a Honda radiator

 

Here is some more pictures.

 

Very nice ... That bike must be very powerful, I would be interested to try a sidecar just to see what it's like , and the seat looks somewhat modified and comfortable.
Alan

 

Hey that's me at the Paris Vintage Rally! Thanks for posting this Lostboy.

 

If you look in the first picture the white Seca beside yours is my bike.

 

Increasing my 750-X motor to 911cc's I always suspected could use larger carbs, so last year I acquired a set of 900 Seca carbs. They are 35 mm versus 34 mm for the 750-X. I cleaned them up, replaced the fuel stop plungers and installed a commercially available Stage-3 jet kit. The only problem I expected to encounter was the insertion of the larger carb bodies into the Maxim-X carb boots. This year I finally got around to this project only to encounter an abrupt dead-end. The addition of a water pump on the X necessitates longer carb boots than the air-cooled XJ's, there is no other donor for carb boots, however that was not the problem. It turns out the Maxim-X has custom Mikuni carb bodies made shorter to clear the water pump. If you look at the pics it is obvious. Disappointed, I remounted the old 750-X carbs and played around with the adjustments. They are now bang on, the carbeuration is perfect, even the typical flat spot between 5 and 6 grand is gone, smooth acceleration all the way. Really, the larger carb might have helped the top end but for sidecar duty the smaller ones probably deliver better bottom to mid torque anyway. I would say this bike now accelerates as smoothly or better than some OEM set ups. I never did find a commercially available stage-3 jet kit for the Maxim-X but my current set up with help from a local dyno tuner is spot on.

 

Nice ride!

DETAILS on the engine mods, engine mounting issues, and front fork conversions would be great. LOTS of details............

 

engine mods;
to fit the 87/88 FZR1000 cylinder block I had to carve the 750-X lower cases larger to fit the cylinder sleeves as they stick into the lower cases.
I went from 68 mm bore to 75 mm!
The water pipe mount between cylinders 2&3 is different on the FZR vs 750-X. The FZR block was welded up, machined down and new threads tapped to accept the water pipe.
I trial fit the motor with piston 1 at top dead centre, greasing the rings and filling the combustion chamber with WD40. Adding the amount of WD40 used to the swept volume of the stroke & bore I was able to determine the compression ratio. I then machined what I needed off the FZR1000 block to bring the CR back to 11:1. The FZR 1000 pistons were actually shorter than the 750-X pistons. Note, this conversion applies to the 750-X (Canadian model) and not the 700-X the USA got. The 700 had the same 68 mm bore but had a shorter throw crank, requiring even taller pistons than the 750-X. If I remember correctly the 700-X had only a 48 mm stroke so combining it with the FZR1000 piston might require more shaved off the block, at some point you might need to worry about cam chain tension.
So my larger 911-X is actually physically smaller than the 750-X.
The 650 Seca gear change mechanism bolted right on to get the gear change to match the rear set pegs of the Seca.
The engine mounts at the rear of the motor required 10 minutes with a file to fit. The front mounts fit.
The base of the gas tank had to be pushed in to clear the taller valve cover.
TCI unit from the X installed.
Cam sprockets slotted and intake and exhaust cams positioned for best mid-range.
There you have it!
The front forks, wheel, calipers and fender are right out of the YX/FZ600 and slip right into the Seca triple tree.

 

Hey, really like the front headlight. Was it difficult to add that to your Seca? I would like to use a large round bucket for a 82 Seca750 Brat Im working on....Thanks! Brian

 

His came that way from Yamaha. There are threads on here about changing to a round headlight. Do a search .

 

I'm curious. Did you ever try the standard 750 motor and decide not enough power? I'm massively impressed by my FZ750, but then again I'm not hauling a chair..

J

 

This bit of your question confuses me. The Maxim-X is essentially a FZ750 top-end on XJ900 cases.
Are you asking if he considered using the airhead XJ750 engine, or the FZ750 engine?

 

My bad. thought thought the X engine was the same as an FZ750, which to me is pretty racey (Maxims are import only here).. I wasn't thinking of the implications of shaft drive etc..

 

as k-moe stated, The Maxim-X is essentially a FZ750 top-end on XJ900 cases.

I've thought about playing with FZ or FZR camshafts, but if there is a difference I probably already have the best cams in the Maxim-X for sidecar duty anyway.
I'm stuck with the X head as the FZ/FZRs had the inclined motor and downdraft carbs. I haven't done anything to my head, the shape of the combustion chamber is not ideal as there is a step where the 75 mm diameter block meets the 68 mm diameter combustion chamber. This could have been smoothed out with a Dremel.
As I learned this spring I'm also stuck with the X carbs, however really happy the way it's currently running.
I put the sidecar on a standard 650 Seca in 1989. In 92 I put the 750-X motor in. In 2000 I put the FZR1000 block in it.
I used to have a Supertrap 4-1 but once I put 16" wheels front and back I lost about an inch of ground clearance and ended up smashing the pipe flat on the bottom over speed bumps. Since then I put an exhaust together with XJ750 head pipes, XJ650 turbo collector, then a custom elbow to mate the Supertrap silencer. I got at least an inch or more of clearance back.
A lot of people ask, Seca-X, when did they make them? I'm never sure where to start.

 

How did I miss this thread? Right up my alley - I've also got a 750X motor in a 650 Seca frame. Here's my thread: http://www.xjbikes.com/forums/threa...-put-an-x-engine-into-a-650-seca-frame.42248/
I think we've crossed paths before on a previous forum. Glad to see that you've still got the bike and it is still keeping you busy. Project bikes are never finished!

 

Hey Quixote, I just recently joined this forum so I missed your posts in 2013. For some reason your pics didn't come up, could be our work system here while I'm on lunch. Really curious to see your bike.
Interesting to read your approach to the cooling as I remember dealing with the same dilemmas. I used a Honda thermostat housing which had no filler neck so it fit neatly inside the frame neck. It's still the highest point in the system so I need to hoist the front wheel on a stand to fill the coolant. I wouldn't worry about the smaller drive shaft of the Seca, something I wasn't even aware of but if mine stands up to sidecar duty a solo bike should have no problems. I've pushed this thing past 160 kph with a friend in the chair, (yes he's still a friend). With the standard 650 Seca powering the sidecar my top speed I think was about 130-140 kph but I had to kick it into 4th as 5th was too tall to pull.
I found some room with the 650 Seca airbox but I had to shorten the connectors between the carbs and the airbox but had trouble sealing them so eventually went to the foam Uni filters like you. Currently running Chinese pods scrunched to fit the frame rails, it's never run better than present. My bike (the red one) came with electronic tach so that was one less thing to mod.
Let me know when you're ready to tackle the 911 big bore, I'll keep an eye out for good pistons and block.

 

I've recently upgraded my cooling system (again) and I think I've got it right this time. I had a new custom rad made, even bigger than the last one. It still doesn't have a fan, but there is now room to put a small one on each side outboard of the frame tubes if I need to. So far I haven't needed to, but then again I haven't really tested it in slow traffic on a hot day.
Besides putting in a bigger rad I also made some changes to reduce heat transfer to the rad when the bike isn't moving - I wrapped the header pipes and re-routed the return line from the rad to the water pump so that it doesn't route right between the header pipes like it used to.
This iteration of the plumbing has eliminated the stock thermostat housing in favour of one from Summit Racing that uses a Chevy thermostat. Bigger than necessary but it works, and as a bonus it's shiny. Under the tank is a wye made from copper plumbing pieces to join the 2 lines coming off the engine into one larger hose to the new thermostat housing. That fitting is also drilled and tapped for the temperature sensor.
The filler is now directly on the rad, on the right side so that it is the high point when the bike is on the side stand.
Also, there is a bit of genuine Canadian engineering in there. I wanted to make a rubber mount for the rad for vibration isolation and the solution was to 'machine' it out of a hockey puck
Still to come: a new overflow tank to replace the stock one which currently lives where the air filter used to be.
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And thanks for the offer of to look out for big bore cylinders and pistons, but I'll pass on that! You deserve to be the only one who has those bragging rights.

 

Does the fender not kiss the rad under hard braking?

 

No, but it's close. Less than a quarter inch clearance at full suspension compression.

 

You have an astute mind k-moe. My fender has fouled my Honda rad after landing some sloppy wheelies riding solo without the chair. The scratches buffed out. I may have extra clearance from Al's bike with my 16" wheel. You might want to add the oil cooler Al if you're still boiling coolant.

 

Some of those pictures make the clearance look worse than it is. Here's a better angle.

 

I just found this photo surfing the net.
I took this photo around 1999 I think. I haven't lived in that house since 2001 so its going back a while.
It was still a 750 here, before I put the FZR1000 block in. I replaced the Maxim-X valve cover with the FZR when I did that and this pic still has the X cover. I powder coated the crank ends black then to.
Also had the complete Supertrapp header back then. Now I use a Turbo collector and XJ750 head pipes.
Back then I still rode this as a solo bike without the chair.
This is the money shot but the pipe is always hidden by the chair.
I think this is about as close to making your 650 Seca look like a Lawson Replica and appearance wise all I changed were the wheels and front fender.
This is basically what I want my Turbo I'm working on to look like. Pipe will be exiting on the left though.

 

Nice pic! But then I would like it - other than the colour and the wheels it looks a lot like mine. I even have the same Supertrapp.
Where did you hide the coolant reservoir?

 

I used 1/2 litre bottle container (I think it was from fork oil) and hid this under the seat.

 

I was just going through my old mags and found the Cycle Canada article with my bike in it.
Nov/Dec 1993, hard to believe this was 25 years ago.
I've made a few changes to the bike since this article.

 

what color is that, really. kind of liking pale mint with dark green stripes

 

I had an antique car calendar hanging at work when I decided on the color.
There was a 55 T-Bird which influenced me.
I think what I love most about the 50's autos were the wild pastels.
Even cream pink is cool but I don't have the balls to paint anything that colour, LOL.

 

I dug out my old files from the dyno runs I did with this bike from 1992.
This 1st graph are the results I got with stock 750-X motor and jetting with pods.
The top curve is torque and the lower curve is hp.
Typical of bikes running without the airbox they fall flat at 5,000 rpm.
It maxed out at about 76 hp but the dip at 5,000 was terrible for pulling a sidecar



This 2nd graph were the results after I got professional help.
Changes included alternate jetting, softer slide springs and drilling the holes to the diaphragm chamber larger.
The drop off in power at 5,000 disappeared and this is mainly corrected by the softer springs.
Peak hp climbed to 82 hp, this is actually better than what I've seen stock FZ750's achieve.
(the 1st run was a Dynojet model 100 dynamometer and the 2nd run was a 150, whatever that matters, both graphs are 4th gear roll-ons).
Since this I installed the pistons and cylinder block from the 87/88 FZR1000. Other than mixture screws and synching I haven't made any further changes to the carbs.
Never put it on a dyno in the 911 configuration, always been afraid of blowing it up.

 

Wow that's a big hole in the "pods" graph. I wish you had one with the stock intake for the purpose of comparison.

 

Here's one for the FZ750 (note it has an aftermarket exhaust, but stock jets: green plot line). Numbers will be different, but the curve shape will be nearly identical to the stock Maxim-X.
4102.pdf
Also keep in mind that (as with most test equipment) the numbers you see for a machine on any given day, and a particular location, will not necessarily be identical to those measured on a different day or location. The overall curve shape should be near identical however.

 

Hey Moe, that's for an XJ750 right? Stock they're listed as 82 bhp, I have an '82 just wondering.
Cheers, 50gary

 

The part number K-Moe referenced is an XJ750 but the fine print states 'This graph shows a typical gain with a Dynojet jet kit.'
They depict typical gains for an FZ750 but it is purely sales embellishment. There's no way in hell you're going to see almost 100 hp from an FZ750.
I used to attend a lot of rallies in the early 90's and a Dyno was always present, I knew the operator well, he's actually an Iron Butt Rally winner.
I saw just about everything on the dyno back then. An XJ650 was typically 48-50, XJ750 55-58, this is rear wheel hp, delivered through a shaft drive.
Other bikes I've owned and put through dyno runs, 87 CBR1000 - 110hp, ST1100 - 88 hp, VTR1000 stock 100 hp, then Yosh slip-ons and Dynojet Stage 1 104 hp.
I paid about $1600 for those 4 extra horses on that VTR, LOL!

 

When I first installed the 750-X motor I had the 650 Seca airbox hooked up. The X carbs are further from the motor to clear the water pump so I had to modify the rubbers to the airbox to make them fit.
It never sealed properly so that's why I went with the pods. In hindsight I should have tried the rubbers from a Maxim-X, they might have fit, but then again I'm not sure if a 650Seca airbox has equal volume to the Maxim-X air box. I did learn a lot through the process and eventually did get it running great without an air box. Now that I have a 911 sucking through the 750 carbs I'm getting really great response, even at 4 grand I can roll the throttle on with a loaded up sidecar and it pulls real strong without any hesitation.

I would expect a stock XJ750-X on a rear wheel dyno would be somewhere between 75-80 hp. It will be less than an FZ, 34 mm down draft carbs and chain drive being advantages.

 

I referenced the shape of the curve, not the total HP,

 

Absolutely, that’s what is important, as you already said different dynos on different days give varying results. People need to realize hp delivered at the rear wheel is much less than sales literature at the crankshaft. Air pressure in the rear tire will affect results.

 

Horsepower is only a result of a mathematical equation (for the nerds out there, here it is. [RPM * T] / 5252=HP, where RPM is the engine speed, T is the torque, and 5,252 is radians per second. That 5252 denominator is the reason every horsepower graph crosses the torque line at 5252 rpm) Torque is all that really matters, and the space under the torque curve is what shows you what an engine can do. A wide, smooth torque curve makes a useful, powerful engine. Peaks and valleys are not your friend.

 

I can't debate Matt's math because he's correct.....but I will be happy to put my '75 H1 up against any non-turbo XJ 750cc or less to show that peak HP is sometimes very, very good if you know how to keep it in the powerband.....the little 500cc green one there in front.....one very badass bike! I didn't spend much time with the appearance as the jewel in this build is the engine was a test-bed that combined several porting mods that worked so well together, it's never been taken apart since.

For the masses though, of course you're right....us 2 stroke guys are an anomaly today....

jeff

 

I noticed my final drive started leaking oil so I pulled the drain plug to see how much oil was still there.
Still lots of oil but I found a spring clip from one of the oil seals stuck to the magnet on the drain plug.
Rather than begin repairing it I just replaced it with a spare unit I had on hand.
Finish is not up to the standard so that's work for another day. The black does look better

 

Hi, stupid question time. To do this conversion needs a 750x head, fzr 1000 block? Could these go on a xj900f bottom end? Is there another genesis engine with horizontal carbs?

 

The point of the question is that firstly 750x heads are scarce around here. And I'm wondering if this lot will fit in my 900f project frame.
Maybe I could fabricate or rather modify the 1000 inlets inlets to make the carbs horizontal?

 

Apart from better engine temp control, and likely more top end power, what are the primary benefits of the X engine over using a 900 Seca engine?

 

Interesting question, combining the FZR1000 bore with the XJ900 stroke would make 1069 cc.
The 1st thing that comes to mind is the water pump. The X has this driven off the clutch basket/shaft.
You would need to use an electronic pump. A quick perusal of the auto world here https://www.summitracing.com/search/part-type/water-pumps-electrical
a lot of these pumps are 10A so that wouldn't work but I did see one at 6A, still a lot for the puny output of our XJ's. Hiding it might be difficult.

Things I don't know - are the wrist pins for the Genesis same diameter as the XJ's?
The stroke is only increasing by 4.5 mm (XJ900 60.5 Vs FZR1000 56) so the pistons are only poking into the barrels 1/2 this, you might need a shim at the base gasket.

The 700X/750X is the only one.

I could source a head for you that's not a problem, I believe the heads of the 700X and 750X are the same.
As far as I know Canada is the only market for the 750X but they are really common here.
To get my 911X motor into the 650 Seca frame I have to remove the valve cover, then there is just enough clearance.
I'm uncertain if the 900 frame gives you anymore room.

You said it - more top end power!
The 900 redlines at 9500
700X at 10,000
750X and FZRs 11,000
higher compression to.

 

Perhaps you could use the idea of Roland Eckert? When making a street legal race bike based on the CB900/1100F engine, finding the alternator making the engine too wide, he moved the alternator further back and drove it via belt https://www.motorrad-fuchs.com/en/single,979,,Eckert_RE1.html

Somewhere on the XJ900 engine, there should be a rotating point to power a water pump. Cam shaft, for instance, for which I know there are pumps for other applications. If it is worth the effort is another question.