First Startup - Won't Idle

Bike is back together and did the first startup over the weekend. Fires immediately and will run with the enrichener on but as soon as I turn that off it will sputter and die.

Little background:

• Head is fully rebuilt. Lapped valves and new seals.
  
• Compression is ~148 +/- 2PSI on all 4 cold
• Shims are in spec
• Carbs have been to the Church
• Fuel levels checked
  
• Full factory airbox with brand new intake boots and manifolds
• Stock everything

Like I said, it will fire instantly and warm up well but as soon as you kill the enrichener, it will sputter down and die. It's not a matter of adjusting the idle stop, I have my carbtune hooked up and you can see the vacuum drop if you thread it in too much and open the butterflies past a normal idle position. When looking at my colortune, you can see the blue flame is very weak and dissipates to almost nothing when it dies. I've sync'd the best I can with it dying off.

Any thoughts? All my thoughts say carb issue but they should be good.

 

First thought is the sync is way off. That's why it is important to bench sync carbs before installing.
Its possible the pilot jets are still plugged or mixture screws are still closed. They should be open 2 1/2 turns to start.
If your carbtune shows the sync is close and idle mix is open then the pilots are plugged.

 

They were bench sync'd. You can see on the carbtune that they are pretty close when you close the enrichener.

Screws are out 2.5 turns. I've tried 1.5 and 3.5 as well with no difference.

I don't mind pulling the carbs if need be, just making sure I didn't miss anything else.

 

I would pull them again and clean the pilot jets. I use a single small wire from a wire brush, guitar strings also work. Take them out, run a wire through them, spray carb cleaner through the carbs and jets, blow again with compressed air to make sure they are clear. I would also take the mixture needles out before shooting carb cleaner in there. Just to be sure it al clean.

 

my first thought is the pilot jet circuit. it is whats running the bike at idle.
spark plugs new and gaped properly?
can you get it to idle with the idle knob?
bring up the idle if you can then running sync it and recolor tune

pilot jet circuit is hard to clean internal passages because of all the " holes" in it

 

Plugs are new and gapped.

No.

 

I like the bench sync method polock suggests with the final step being to adjust the butterfiles open to the point you can see the first hole in the top of the carb throat.
I adjust mine to where I can see the full hole on each butter fly. which may mean tweeking the individual adjustment screws

 

Air jets reversed?

 

I pulled one hat tonight and they're correct, as in the real correct and not the Haynes correct. The carbs were rebuilt by Hogfiddles so I seriously doubt something is incorrect. It was a year ago, but they were stored dry (never any gas) and in a bag so I don't think it'll matter.

I'll go over everything again this weekend. It's possible I missed something, wife was out of ton so I had all three kids running around and was dividing time. I need to get a few hours to review everything, double check fuel levels on bike etc.

 

You sure there isn't an air leak? I replaced my intake manifolds last year, and it ran like yours does.... fine on enrichment, but wouldn't idle. Turns out the "new" intake manifolds were the wrong size and caused leaks.

 

D@mn sure better not be anything clogging anything in there. If it comes down to it, though, I'll go through them again, and double-check everything.

First thought that I have, though, is the wet-set float levels......

 

I highly doubt it's your work, I mentioned it more to clear up how well the carbs were cleaned

Hoping to get a couple hours in the garage tonight to go over things. Fuel levels were wet set prior to installation.

 

When you have the bike running with the choke on. blip the throttle and see what happens. does it struggle or stall out?
I am guessing its going to stall.

The issue sounds like it's either A: you have a vacuum leak in the carbs/intake/airbox or B: issue with the fuel delivery

spray starter fluid on the intake boots and where the external washers are on the carb. See if the revs jump up.
Also try turning the petcock to prime and open the gas cap

Nothing bad on hoggy, i am sure he did a great job, but if the carb sat for a while and was jostled during shipping something could have came loose or dirt got in and clogged the carbs.

 

Checked float levels again, were close to 3mm. Set them to 2mm, no change. Checked all boots etc for leaks with propane. No change there. I can get it to idle fairly smoothly with the pilot screws out 5 or 6 turns but that seems too far out and throttle response is horrible.

I'll let it cool overnight and check shims/compression numbers tomorrow. If that doesn't do it, I figure I'm getting into the carbs then.

 

The propane trick never worked for me. It always showed no leaks. It wasn't until i used started fluid did i find where the leaks are.
Testing with propane there are too many variables that can limit its effectiveness eg, burping, farting, cross breeze...

 

Intake boot gaskets maybe leaking ...I make my own out of gasket material from auto parts store...no leaks !!! you may want to pull carbs and pull of the boots and check there first.

 

To be fair, I'm using MAPP gas. I pulled a vacuum cap off to test and the idle speed increases when i hold the torch near it. The idea of spraying starter fluid all over my new manifolds and freshly painted/polished everything scares me a bit.

Those are new and show no leaks with mapp gas test.

 

Jay, keep me posted.......if I need to go back into them and correct anything. Shouldn't be, though------

If anything were still in there, and I can't see how, seems odd that it would be affecting all four

Dave fox

 

I think I would get bike synched (running synch) before worrying about using color tune. I re read your post Agree with M-lew the choke is letting more fuel in and is just helping it run bypassing the idle circuit. Because of this color tune is not going to work right, need a steady idle first . I'm 100% positive Hogfiddles did a bench synch this will be close , but you will still need a running synch. Do you have a 4 vacuum gauge for synching? If not you need to build a manometer , using the gauge method on mine I knew I was in synch when all 4 needles are even at 5hg on gauge( does not mater where as long as even)

 

@hogfiddles Dave, thanks for the call! I will continue looking things over today. I too think it's weird that it would be carb related. RPM with enrichener on is about 4500 RPM. Once off, it settles to around 1000 and slowly dies off.

@Jetfixer, yes I have a morgan carbtune. I was able to sync up but the only way she idles is with the pilot screws way out. You can see with the colortune that the fuel is almost non existent with the screws around 3 turns out.

Warm compression test:

1 - 155
2- 158
3- 158
4- 155

Going to check wet fuel levers once again but shes definitely staving for fuel at idle.

 

Wonder if this is causing me sealing issues. Yes they were brand new. I have 3 like this. Even if not, still not crazy about them coming apart internally under vacuum.

 

Shazam ...one other thing to check the fuel tank petcock ..is it still vacuum or do you have an aftermarket? It is possible fuel line is collapsed internally not giving enough fuel..Your compression readings are real good.

 

Oh NO that is not cool sorry ..I was posting at the same time for new intake boot ...

 

Intake boots should not look like that at all. That is a very unusual failure, and I have not heard or seen reports of new ones failing until now.

 

No kidding right? If you had told me specifically to look at my new boots for a failure I wouldn't believe you.

 

I was Reading this post , because I'm busy making my 750 run right... But now I wonder, the mixture screw... I does enriches the idle with fuel right? Or does it cut of air? I have the hitachi's hsc32's with the screw on top..

Thanks in advance for your answer!

 

The idle mixture screw controls airflow, which then controls the amount of fuel that gets sucked up into the pilot circuit.

 

The Hitachis the mixture actually controls the amount of fuel introduced into the airstream, the more turns out the richer the mix.

Ive heard that the rule of thumb is its a fuel screw if it's on the engine side and an air screw if it's on the air filter side but I have not worked on enought carbs to weigh in there. I only know on the fee sets of carbs I have done.

 

It actually controls the amount of flow of the already mixed air and fuel, by increasing or reducing the flow rate. It's a slick system.

http://www.xj4ever.com/inside your carbs.pdf

An air jet that constrains the maximum airflow rate.
A fuel jet that constrains the maximum fuel flow rate.
An adjustment screw that fine tunes the overall flow rate.

 

I guess I should say fuel/air mix but the pilot screw is definitely on the fuel side. I think you're saying it controls the amount of air that goes into the pilot circuit which is incorrect for this carb. Those carbs you screw in to make it richer by limiting the amount of air. Less air = more fuel sucked up. The Hitachi you screw out to introduce more fuel and make it richer.

 

I'm just not being clear is all. We're both describing the circuit the same, I'm just not doing a very good job at that tonight, and mixing up nomenclature. It is indeed a fuel screw.

 

Your edited post makes sense, we're on the same page. I just was pointing out its not an air screw like some carbs have.

Give me about 30 minutes and I'll be there. The guys at work dropped me a growler from a brewery near a site they visited today. I just couldn't let it sit until the weekend. You know how it goes once you crack one open

 

Back on topic though, Chacal went out of his way to make it right and I've got a new set of intakes on the way. I'll update next week with the results.

 

Can't fault anyone for a good growler.

 

It's ok.... We're all screwy tonight

 

Thank you very much for your replies! It makes sense now, tomorrow I will do a first time colortune!

 

iwas thinking of getting new intake boots this scares me away considering the price of them cheapest i have found are from canada $240 posted but might just stick with my shabby ones and i just found these for 70 bucks anyone know if they fit a xj750 http://www.ebay.com.au/itm/80-81-YA...964780?hash=item25b961806c:g:cq4AAOSwwpdW~Mrt

 

They will not. Those are for non YICS engines and while two of them will fit correctly on a 750, the other two won't.
Your old ones can be repaired with RTV. DO a search and you'll find several threads about how.

 

Yeah those look pretty beat. I couldn't find the link I wanted but found this one is basically the same.

http://xjbikes.com/forums/threads/cracked-intake-repair.24552/

Try http://xj4ever.com don't know how much shipping will be???? Send a email see what he says.

 

When trying to search for something on this site I find that a Google search of??? Whatever followed by xjbikes.com works well.

 

I had to chuckle, 'Growler' can have another meaning over here - especially when preceded by the word 'hairy'..

 

It shouldnt. The key is purchasing from a reputable seller in case you do have issues. This is true with many things.

As mentioned though, there are many ways to fix old ones. Mine were too far gone.

 

Update. Replaced the manifolds with some OEM ones and she stared right up and idled with screws at 2.5 turns. Looking closer at the aftermarket ones, they cracked at the motor side, some cracked outside the sealing surface allowing air in.

Looks like a sync and colortune is in order for today!

 

Well-- that sure make ME feel better, too !!! Lol

Dave Fox

 

Not as good as me hearing it run after 2 years!

 

Still working on my idle. How smooth should it be? I keep reading "sewing machine smooth" but it is definitely lumpy and it has been bugging me. Pulled carbs tonight, fuel levels are dead on across all 4. I then sync'd and colortuned. Still cant get it smooth. When using the colortune there really isn't much difference in color between yellow and non existent. Any good videos of a properly idling 650?

 

It'll sound like this.


You say it goes from yelllow (rich) to no color at all quickly. What do you have the pilot screws set to for your baseline, and what directon are you turning the screws when the color drops out?

Are you trying to read the colortune in the sunlight?

 

What makes that "whirl" sound on these bikes ?

 

The alternator. It's chain driven.

 

Thanks for that video, mine wasn't far off from that. I probably should've left it alone.

Regarding colortune, I started at 2.75 out. Doing the tune in dark garage, door open and with fan. I back out to yellow and then back in looking for Bunsen blue. The thing I noticed though is I don't notice much difference in the blue color between yellow and no fire. Takes about 2 turns to go from yellow to not firing, was trying to set it by the way it sounds in that range.