RE-Jetting

I just got a Dyno-jet kit in the mail. Does have step by step instructions on how to do this. I’ve done it many times with car carburetors and once on a dirt bike carb. That was a 100cc two stroke one jug. This is a 81 Seca 750! I have full confidence in my self. Just like to line up as much info as possible. Thanks!

 

good luck, doing it on other vehicles b4 should help, seems the kits arent to liked round here. let us know how it goes!

 

There's not much to these kits really .... basically just remove the old jets, put the new ones in, reinstall the carbs, and see what happens. Unfortunately, tuning carbs likes this means lots of trial and error, which happens to be a serious pain in the butt with how our carbs mount.

 

I'm thinking about re-jetting for pods eventually. I wonder if it would be worth it to fab up an adapter plate to make removal easier? something that can be removed when the process is complete? It would add about a inch or so to distance between carbs and intake. Wonder if it would cause problems...

 

kd5, what do you mean by an adapter plate? I would imagine the extra distance the carbs have to push the fuel (allow the fuel to be drawn?) would have an impact on the mixture ratios....

 

Just some thing that would hold the carbs against the boots with a decent seal. Wouldn't need much strength, you wouldn't ride the bike (much? at all? I'm not sure), just something to let you 'set' the carbs in place, test, remove, try new jets, repeat. w/o the struggle of getting them in to/out of the boots.

My first though was something you install the same way as the carbs, actually into the boots, that holds the carbs against a plate with soft rubber seals. The carbs wouldn't seat into the boots, so whatever distance that takes up, that's how far 'back' they would be. Plus the thickness of the plate/rubber seals.

Add some rubber straps or metal clips to hold the carbs to the plate.

Pop the clips open/remove the straps and the carbs would basicly fall off the bike. Much easier than the 5min it takes me to remove them (not to mention install them).


Another thought is a soft doughnut type of seal. Use one on each carb and it could seal between the carbs and the boots. Holding the carbs to the bike would be a little more difficult.

Thoughts?

 

sounds like a cool idea .... i'm just not sure how practical it would end up being. with the airbox in there, theres not much room to spare.... if you were running pods i could see it a little more easily, theres alot more room in the back for various straps and whatnot that way....


Not sure ... would love to see a mockup =)

 

lol someone hijacked the thread i say that if you're gonna be tearing into the carbs, get a new exhaust and soem pods

 

Shooter:

Before you make a personal recommendation to have other Members modify their Bikes ... either include all the necessary precautions and decisions to be made BEFORE carrying-out your recommended Mods ... or,

Don't make any recommendations that you do not know how your recommendations will effect the other Members Bike ...

AND ... what to do to restore the other Members Bike to a Tuned-up and running condition AFTER they do any Mods you have told them to do!

Installing Individual Air-Cleaning Pods and Aftermarket Exhaust Systems often require many hours of experimentation with the Re-Jetting of the Carbs to offset a Critically Lean Condition that could potentially ruin somebody's Engine.

Please don't give advice to other Members on matters of Mods and Tuning.
Your inexperienced advice might cause the other Member to try or do something that could prove to be a very expensive mistake, or worse, one that cannot be undone!

 

yep you're right.... just figured he knew what he was getting into, and he'd still has lots of adjusting to do, and i guess jsut stating my opinion... but ya sorry

 

kd5; Your idea has one serious flaw: By doing that you will effectively be lengthening the intake tract from the carbs to the combustion chambers, that WILL affect tuning. You can probably get close, but when you plug the carbs into the boots fully, it will change eveything. How much is hard to tell. I would also be concerned with not getting a good seal and sucking air where you shouldn't. Nice idea, though.

 

When I got the bike is was in pieces. Actually it was 1¾ bikes. An abandoned restoration. It already had a megaphone 4X2 pipe. After I got it running, I had it at a bike shop. They said it was tuned fine, but was running lean at mid to high RPM. The jet kit has two sets of jets. One for mild pipes and single elements air filters, and a second set for more wild mods. I intend to run the factory air box with a K&N, so I’ll stick with the first set and see what the gas analyzer says. Thanks for all your inputs.

81 Seca 750

 

One suggestion... Try to avoid using the dynojet needles. The taper on them is not a good match for the stock Y13's... The have a tendency to create flat spots in the throttle which are a major pain to tune out. If you're running a bit lean mid to high, try bumping the mains one or two sizes (maybe 124?).

also, check for leakage in the throttle shaft seals, cause they can also add to the lean-ness.

just my $0.02USD

 

I do have a bit of experience in this type of mod. I just did my XJ900 Seca with air pods. As I'd mentioned earlier, I solicited advice from others who'd done it successfully and the most common recommendation was 120 size main jets, up from 102.5, size 42 pilot jets, up from 37.5. The needles are raised as high as possible. I also put on exhaust cans with the end baffles removed. The key was using a Carb-tune II synch tool and a color tune plug. These allowed me to synch the carbs perfectly and adjust the idle jets exactly. This resulted is the idle jets being set at between 3.25 to 3.5 turns out from seated. After all that, the spark plugs are a nice tan color, not too rich and not too lean. Throttle response is excellent at off idle and through-out the rev range in all gears. Maybe I was just lucky but I think the combination of having the benefit of other people's experience and using the right tools made the difference. As Rick says, the important thing is too avoid an overly lean condition. You're introducing much more air into the engine using the individual air filters, so you have to introduce more fuel. Finding that balance is critical. I have to warn anyone who tries this that I did the job on a 1983 XJ900RK Seca. The parameters would be quite different on an XJ650 Maxim, for example. The needles in the Maxim's Hitachi carbs don't have clip slots to be raised or lowered. You must use brass washers to raise the needles. That's just one example of the difference in bikes. I'd say the main thing is to do as much research as possible before beginning this kind of project and solicit the opinions of people who've completed it successfully.
thx,
baz

 

Thanks BAZZ

This is what I was hoping for! Thanks for the info. This is not my first bike, but is my first bike restoration. I was a semi-professional Hot Rodder back in the day, so the details don’t frighten me. I got it back together and runner pretty good on my own. Then this lean condition came along. I’ll get it right, I just have to keep at it. Thanks for everything guys!

81 Seca 750

 

Hey Danmar,
Glad I could help. I think the key is patience. It took me quite a while to find out exactly what I needed in terms of jets and settings. I began by going up to 107 sized main jets and they were far too small. So I wasted some money on a set of main jets. Synching the carbs took quite a while. I'd get the carbs nice and even, give it some throttle and they'd go out of balance again. It took countless tiny adjustments to get it just right.
Basically, you're synchronizing #1 carb to #2 carb with the adjustment screw between the two carbs, then #3 carb to #4 carb with the adjustment screw beween them. Once those are balanced to each other, you synchronize the #1&2 carbs to #3&4 carbs with the adjustment screw in the middle of the carb set. Your idle will probably be kind of high by the time you reach this stage so you turn it down using the central throttle screw behind the carb set. I had to go through this process quite a few times to get things just right but it was worth it in the end. Now the bike starts and warms up nicely on a little bit of choke. Afterwards it idles smoothly at 1100rpm and revs nice and clean.
Yup, as I said, patience is key.
thx,
baz