still haven't got a good carb install

Guys, just like the other thread, I thought I was a ok mechanic until...

this might be my 4th thread about this - sorry

New coils, wires, plugs, plug caps, rebuilt petcock and carbs.

Now I have exactly what sounds to be an air leak - after a rev off idle it takes a while to come down to 1050 RPM, but not if I rev it a little, only a bigger blip, like up to 3500 or so. Did the propane test, carb cleaner, and starting fluid test - sprayed all 3 (at different times) on the carbs to see if the idle raises and it doesn't. I hear occasional surges through the #1 cylinder but I'm sure that'll clear up once I figure this out.

Sometimes it'll rev up when i turn the throttle and someimes it'll just sputter, even if I hold the throttle wide open. 2.5 turns out and fuel levels are good. What happens if the fuel level is 1 or 2mm low? I'm going to buy a plug gapper now even though they come pregapped

This is Months of effort, please guys help me

Thanks for all your comments

 

Check your carb boots?? Thats what I think is doing the same thing to mine. My #1 carb boot is hard as a rock and doesnt seat properly on the airbox. Got it elec taped up.
-slk

 

THANKS SLK. bump for the guru's. Going to try the electrip tape thing now, or some funtak or somehting. here's a pic of the crack

 

Take the top off a tube of Black Silicone RTV Sealant.
Squeeze some out on to the tip of your finger.
Wipe that leak and seal it up.

 

Have you clunk tested your carb slides? Sticking slides will slow it coming back down to idle.

Also, your throttle cable. Does it have freeplay in the cable, at the throttle butterfly linkages when the throttle is at the idle stop. I know I did this once, and couldn't work out why it idled at 2000rpm.

 

Nope, I used funtack to fill in the crack, very nice seal. gapped the plugs better, they were Above tolerance, 35mm instead of the 32 max.

the clunk test never failed on it, even when I opend the hats the first time. the cylinders drop heavy and if I made the diaphram seal they lower slowly

Railtrolly, when your cable was hanging up at 2grand, did it eventually come down like mine?

It ran a little better, ideled high at 2 grand instead of 4 or 5 before coming down to 1050 normal. then after running for 2 mins, back to sputtn and no possible throttle advancing.

so it sat for 4 hours sinc the last its last run, so maybe the gas dryed up and then ran good until the cylinders filled up too much again? I guess I'll let it sit again and possible dry the flood, and see if it does that again.

So a question from the thread starter, what does it mean if you hold the throttle wide open and it just sputs? what if the fuel level is 1 mm low?

Someone told me it could be the head gasket, but it looks fresh with all the red RTV squeezed out

Thanks ya'll

 

Hey yeah that sounds about right. Checked your idle mixtures? if you're at idle and your cylinders are gettin too much gas, but not enough to foul em up, it could just be revvin high to burn it off.
What are your idle mixture screws set at?

 

2.5 exactly

 

Yarraman,

My engine did not come down from 2000rpm, although the high revving scared me so much I shut the engine off before I could see if it was going to come back down to 1000rpm. I took the throttle cable off again and noticed that the throttle linkage dropped down further, so the cable was just pulling on the throttle. Adjusted it at the handlbar turnbuckle until there was a bit of freeplay, and now it idles just over 1000rpm, and drops striaght back to 1000rpm after revving the engine.

I had just cleaned the carbs and put them back in the same way, so I don't know how the cable tightened up.

 

35mm? Not possible.

Are you talking about 0.035 inches?

Gap tools are in inches (0.20~0.100) and metric (0.45~2.55)

You should be closer to 0.028 inches up to a max of 0.032 inches, the gap expands with age so set to the 0.028 and go from there.

Have you sync'd the motor yet, and colortuned, then resynced and recolortuned?

Without going through that procedure, revs and motor reaction etc are pointless to diagnose anything.

A motor can BARELY run, and hit the throttle it will climb to 8k, a simple sync and colortune session and it can run perfect, react sharp, drop quick, etc.

 

OK OK I'll get the damn colortune! Thanks all

 

by the way, I used funtak to seal up the airbox crack and it got a little better. now it just sputters a little under 3k. Funtak is that poster hanging stuff, found it in Target for 2 bucks. real easy application, easily removed, and you can color it if you need to, no mess

 

yama

Keep an eye on it though. I have a sneaking suspicion it might harden and crack. I know the stuff you mean - over here (and in UK) we call it Blu-Tack (made by Bostik). Handy stuff around the house but heat might affect it.

 

good good point, thanks! good thing it only took up 5% of that 2 dolla package!

 

Hi guys. I know this post is 6 months old, but I just purchased an 82 XJ750 and am having a similiar problem. I have been searching the site and found this. My bike will idle, but when you crack it, it is very slow coming down. A mechaninc friend of mine thinks that it is the lip seals on the shaft that runs the butterflies that are going bad. I took the seal out of the outstide carbs, and one looked a little cracked. Before I go tearing them apart and attempting to find the seals, I was wondering if the colortune helped you yamaman, or if you have come to a conclusion.

 

i quess this post isnt that old. i was looking at the wrong date. sorry guys. new here

 

That 28 Year Old Bike might need to have its Carb Diaphragm Piston Bores
De-Aluma-Oxified.

Conduct test for an air leak.
Use Carb Cleaner or Starting Spray.

If no leaks are detected ... Re-finish the Diaphragm Piston Bores within the Carbs.
Please read this article I published on the matter some time ago.

http://xjbikes.com/Forums/viewtopic/t=1 ... +test.html

 

Paulsen, my damn ignition switch broke so i'll be posting the results another day. After all this I think I still have a few things working against me, maybe my float valve needles are leaking really slowly and my fuel filter was lying horizontal and might not have been letting the air bubble out. But I can say be sure you're completely sealed up on the intake end, even the front of the airbox lid, everything. or run the bike with all the carb vacume ports closed with good rubber caps and the petcock on Prime, but not for long!

 

I tried the spray test. boots are all good, but a couple of those shaft seals are in fact leaking. thanks for the link RickCo, very informative.