Vm33 smoothbores

[Fjbj40]

I have a set of these on my 78 gs1000 which has a Yosh 1085 kit plus porting and polished head.

The carbs were just completely rebuilt as was the engine and bike. Just fired it up and it is not firing on #3. I swapped the the wires for 2 and 3 and it still does not fire. Tried a new plug, still no go.

One thing with the carbs is there is also a fuel inlet for a fuel line on #3, I just have it capped. Is there supposed to be a fuel line hooked up there also along with the feed in between 1&2?

I cracked the bowl drain for #3 and fuel drains. I adjusted the air screw and no luck. Gave the carb a few raps thinking maybe it would help but no.

Help?

Thanks,
Daryl

 

[Katarat]

Plugged pilot jet

 

[Fjbj40]

Plugged pilot jet

After a little more thoughts came to the same conclusion. Fired her up again and she makes heat from about 2000 and above.

Still need to know if I need the extra fuel line hooked up?

Time to pull them

 

[ozman]

After a little more thoughts came to the same conclusion. Fired her up again and she makes heat from about 2000 and above.

Still need to know if I need the extra fuel line hooked up?

Time to pull them

a pic of your carbs would be handy
the fuel lines usually go onto 2 and 4 they are larger fittings than the vent line fittings which are on 1,2(is capped) and 3 but not on 4 on my 33's
some sets use a T between 2 and 3 for fuel line and the fittings on 2 and 4 are plugged
but it sounds like blocked pilot jet if the cylinder fires up at over 2000 rpm

the bigger fitting in rh side pointing up is fuel in
the smaller fitting on lh pointing back is vent



showing T fuel fitting this set is 29mm but i have same setup on a set of 33mm


ozman

 

[Fjbj40]

a pic of your carbs would be handy
the fuel lines usually go onto 2 and 4 they are larger fittings than the vent line fittings which are on 1,2(is capped) and 3 but not on 4 on my 33's
some sets use a T between 2 and 3 for fuel line and the fittings on 2 and 4 are plugged
but it sounds like blocked pilot jet if the cylinder fires up at over 2000 rpm

the bigger fitting in rh side pointing up is fuel in
the smaller fitting on lh pointing back is vent



showing T fuel fitting this set is 29mm but i have same setup on a set of 33mm


ozman[/

Odd, 1&3 is fuel in on mine and 2,3,4 is ventI do not have the T fitting like you. Guess I will put a line on #3 and join it to the one feeding #1.

Mine are a VM33E set.

Thanks a bunch,
Daryl

 

[Fjbj40]

Well pilot jet and passages are not blocked! I hooked up the other fuel line, still no work at idle.

I remember loosening and partially moving the jet block for one of the carbs, just don't remember which one. So I am going to disassembly #3 and have a look.

Any ideas? I swapped #3 and 4 pilot air screws but it made no difference. Valve clearance is .002" on each valve for #3 and it has compression.

Daryl

 

[chuck hahn]

Before you tear it down, poke a small wire thru the hole at the back of the jet block. When you" partially moved the jet block" you may have jostled the paper gasket under it and blocked the port.

 

[Fjbj40]

Before you tear it down, poke a small wire thru the hole at the back of the jet block. When you" partially moved the jet block" you may have jostled the paper gasket under it and blocked the port.

A already tore her down and there was some damage to the gasket so I installed a new one. When I pulled the pilot earlier i blew air through the port and I noticed that it seemed some air was coming from where the slide goes between the body and block.

Will run it tomorrow, I would be shot if I ran it tonight :lol:. I am running just the Yosh head pipe so she is a little loud

Tomorrow will tell,
Daryl

 

[Fjbj40]

Still no work!

Have spark, compression is not where I want it to be, it is 135 psi as is #2. 1 and 4 are 165. #2 fires, so #3 theoretically should at the same compression.

When I look at the cyl side of the carb I notice 3 is hardly open at idle but the others are probably 2-3 times more open. #3 is the baseline for synchronizing. So shoud I open up 3 more and match the others to it then go from there?

Help!?
Daryl

 

[blowerbike]

match the other 3 to the non adjustable carb.
this a a bench sinc and works good.
if 3 is lower then it will not run till the throttle is opened.

 

[Fjbj40]

match the other 3 to the non adjustable carb.
this a a bench sinc and works good.
if 3 is lower then it will not run till the throttle is opened.

This was my thinking. So what would you suggest as an opening, say 3/32"-1/8"?

Thanks,
Daryl

 

[blowerbike]

you find the non adjustable carb.
you run the idle up till you can get say a piece of tig rod to slightly drag under the slide.
you then adjust the other 3 to that one.
then you run the idle back down and start the bike and set your idle to your liking.
this is called a mechanical sinc.

 

[Fjbj40]

you find the non adjustable carb.
you run the idle up till you can get say a piece of tig rod to slightly drag under the slide.
you then adjust the other 3 to that one.
then you run the idle back down and start the bike and set your idle to your liking.
this is called a mechanical sinc.

Done, set it at 5/64ths ", revved high, dialed it down to 1500, still no joy. She does get hot, but not scorching hot like the other 3.

Think I will give it a road run and see what happens

Daryl

 

[blowerbike]

without going back through this thread....
have you checked/replaced the o-ring on your intake boots?
have you checked for leaks?

 

[Fjbj40]

without going back through this thread....
have you checked/replaced the o-ring on your intake boots?
have you checked for leaks?

They are Mikuni boots, there are no o-rings. It just mates to the intake manifold.

I will switch 3 & 4 intakes and see if the problem follows.

Thanks,
Daryl

 

[blowerbike]

They are Mikuni boots, there are no o-rings. It just mates to the intake manifold.

I will switch 3 & 4 intakes and see if the problem follows.

Thanks,
Daryl

check for leaks.
i always silicone those type of boots.

 

[Fjbj40]

check for leaks.
i always silicone those type of boots.

I siliconed when I installed them. Will pull and check for cracks and reinstall if none found.

Stay tuned

Thanks,
Daryl

 

[Fjbj40]

I pulled all boots, checked them and no cracks or leaks. Reinstalled them with permatex and swapped 3 & 4.

No change!

Screwed pilot airscrew in tight and that seemed to improve it a little. Cranked the idle up to 3500 rpm and started whacking the carb bowl with screwdriver handle and it hiccuped and speed changed a little.

Shut her down and did a compression test with carbs removed. 1 to 4 are 160, 160, 125, 160. So I suspect it is a mechanical issue and not carb related.

Fawk

 

[Fjbj40]

Problem solved :dancing:

It turns out that the vent on #3 is not a vent. It is the vacuum source for the fuel petcock.

Soon as I plugged it she purred, and when you crack it it breathes fire
This is going to be a monster.

 

[blowerbike]

yeah major vacuum leak on the dead cylinder.
makes sense.
at least your carbs are in sinc now:lol: