you can't spell stupid without SU.....

[wfothrottle]

ok
i'm at my last straw........

i have one of those Hif SU carbs.

the bowl is filling up with gas, but it's not putting any gas down the manifold.

i pulled my carb off the other day because i haven't gone through it after it was sitting for 5+ years.

it was running, but it wasn't running very well and decided that last weekend was the time to pull it off and go through it.

it didn't look bad at all, the float needle looked a little iffy but it wasn't leaking so i cleaned everything up and put it back on.

after i put it back on the float bowl was leaking, and i ordered an new seal along with a new float bowl needle and seat.

put it back on again and nothing.

i crank and crank and crank and crank.........

nothing.....

spray some carb crap in the carb, and it fires. then dies when it runs out.

pulled it off again, go thorugh it really good. put it back on, and nothing.
crank and crank and crank........
nothing.
spray some crap in the carb and it fires, then dies when it runs out of gas.

pull it off AGAIN, go through it really good AGAIN. make sure EVERYTING is blown out and clear and clean.

put it back on.....nothing.

i repeat 2 more times with the same resolve.

i don't understand. the bowl fills up with gas, the pump pumps there's gas in the tank. and everything in the carb is clear and clean.

does this sound familiar to anyone?

i'm about ready to pull it off and smash it with a hammer, but i don't have the money for another carb and if i was to buy another one it would be a weber....

[joltfreak]

did you check to see if the needle and float are moving freely? also is the jet adjusted properly?

[wfothrottle]

Yeah all thatstuff.....I've rebuilt lots of carburetor's, and haven't had any problems like this.
The bowl fills up but no gas goes into the motor......
I don't understand
There's a couple things I'm going to try.
I'm going to try some fresh gas, and look to see if I knocked a vac hose off somewher.........

I just don't want to spend $20 on gas for something that isn't running.

I have the next couple of days off, I'll posts what I find.......

Or I'll post a flattened carburetor for sale

[Willie_B]

Remove the dashpot and make sure the needle on it is still attached and able to move around a little bit. Oil in the dashpot and that it moves smoothly up and down and not catching.

[wfothrottle]

There both good.the needle wiggles around and the dashpot moves up and down smoothly.
The only oil I have besides 20/50 is 5 or 10/30. Which seemed to work fine before.
I should have time to mess with it today...........
I'll let you know

[Willie_B]

Maybe a massive vacuum leak after the carb so you are not sucking enough thru the carb to pull any gas up.

[wfothrottle]

A vacuum leak would make the most sense, but when I gave it a quick once over,  everything looked fine.
I'll be taking a closer look........

[Willie_B]

Are your intake and exhaust manifolds mis-matched in size on the mounting flange? Just wondering if you have stepped washers to compensate and they may have been put in wrong and the intake manifold is drooping and not sealing. Everything would tighten down but still not seal. Just a WAG  (wild ass guess).

[wfothrottle]

OK.....
The first thing I did was check all of my vacuum hoses, and they all looked fine.
I didn't think to look at my manifold. I'll take a look at that tomorrow.
The next thing I did was to have my wife crank the motor while I checked how much suction I was getting though the carb.......
Not very much.
I had my hand covering the whole opening, and could barely feel anything.
But it fired....
It would only stay running if I kept my hand over the carb and messing with the throttle.... and only for a little while
I'm thinking big vacuum leak...... but from where.....
I'll check the manifold, but I found this and I have no idea what it's supposed to do.
Can anyone tell me why and when this is supposed to work.
I was running out of hands while I was trying to keep it running, but it was sucking air.

[Mudhen]

Are your intake and exhaust manifolds mis-matched in size on the mounting flange? Just wondering if you have stepped washers to compensate and they may have been put in wrong and the intake manifold is drooping and not sealing. Everything would tighten down but still not seal. Just a WAG  (wild ass guess).

This happened to me.  Got new SUs but didn't know about the stepped washers - car started right up fine at first...then once they slipped down, massive vacuum leak and no more starting.  Never did figure it out - had it towed to a local British car place and they found it.

Good luck wfot.

[wfothrottle]

thanx willie b and mudhen.
i was looking around and would the step washer be the washer that the intake and the exhaust manifold share?

if so it doesn't have a step washer there.
and i never took the intake off.....

the intake is tight and sealed to the head and the carb is sealing on the manifold.
i have a massive vacuum leak, and i can't tell from where.

i have a hard time believing that something else failed at the exact time i pulled and rebuild the carb

[Mudhen]

When you have it running a little can you spray some carb cleaner around?  If it finds the leak the revs should go up.

Did you chase the jets with a little wire or something?  The cleaning could have lodged something in there maybe?  Not sure you can do that with an SU I guess...had to do it a lot on the triple Mikunis on my Tiger thanks to Ethanol.  Seafoam was my friend.

When is the last time the jet was replaced?

(Note I really suck at diagnosing anything other than an empty beer glass but just some stuff to think about)

[wfothrottle]

beer has been my only friend during this ordeal.....
maybe that's my problem.

i know it has to be something stupid, i just don't know if i'm smart enough to find it

[Mudhen]

thanx willie b and mudhen.
i was looking around and would the step washer be the washer that the intake and the exhaust manifold share?

if so it doesn't have a step washer there.
and i never took the intake off.....

the intake is tight and sealed to the head and the carb is sealing on the manifold.
i have a massive vacuum leak, and i can't tell from where.

i have a hard time believing that something else failed at the exact time i pulled and rebuild the carb

I was thinking that collar was carb-to-intake...but it is intake-to-head.



Light bulb came on, too, why I never thought to put it on - my old setup didn't need it because the intake had slots for the head studs:



So you may not actually need it at all anyway...

I'm going with clogged jet.  Final answer.

[Mudhen]

Hey WFO - any update to this?  Hopefully you got it solved so are out enjoying driving it instead of busting knuckles...