Vacuum Leak,

[kablea]

Howdy all

i think my GQ 4.2 carby has developed a Vacuum leak in the manifold area somewhere.
wondered if there is a common area to look or if i needa rip it all apart and replace all gaskets and seals. (i Surley hope not :icon_bonk: ) lol...

thanks
Aaron.

[AB]

Hi Aaron, you can spray around the manifold gasket when your engines running with a can of water dispersant to find out where its leaking.

If theres a leak then it will suck it in and your engine will rev slightly higher too then you know where the problem is.

[patch697]

Ok there is a simple way to find this if you have one......

Grab yourself a can of CRC or WD40 (with the little tube) & spray around the gaskets, vac hoses & joins (not all over the place just one area, join or vac hose at a time). If you have a rough idle coursed by a vac leak it will smooth out if you hit the leak until it sucks up the spray then it will start to idle rough again & to confirm spay it again & it should do the same & you will have found your leak.

Good luck

Cheers
Paul

p.s Good onya Andy no posting what Im posting.......lol

[AB]

p.s Good onya Andy no posting what Im posting.......lol

Beat ya!!!

Same time though, mustve just snuck in..haha

But yours is probably better as everyone has wd40 or crc...hahaha

[patch697]

Beat ya!!!

Same time though, mustve just snuck in..haha

But yours is probably better as everyone has wd40 or crc...hahaha

It all works the same way in principle so yeah what he said to kablea.....lol

[kablea]

lol... Thanks Fellas.

i'll give it bash when i get home

Aaron

[kablea]

Howdy guys,

I spent Ages checking every gasket, hose, ect ect ect... stil no luck... But one thing i did notice is if i take one of the vac hoses off the manifold, the idle jumps up and she seam to run good, cept for the 1100 Rpm, on gas,

But on petrol, she wont idle at all ever... with out a bit of throttle. Vac hose on or off seamed to make no difference.

So i'm thinking it might not be a vacume leak. :icon_bonk:

Any advice would be great. Cant get it to my mechanic for a week... so i hope i can fix it this w/end. or at least figure out what it it doing...

Thanks In advance
Aaron.

[patch697]

Without see it in person I'd say the carby sounds like it needs a rebuild. What you have described is not an uncommon problem with TB42s running duel fuel & I've come across it quite a few times.

Cheers
Paul

[Finly Owner]

Hi and welcome Aaron. Do they have a PCV, it may be blocked? or am I totally ooff track? head tired tonight.

[kablea]

Hi and welcome Aaron. Do they have a PCV, it may be blocked? or am I totally ooff track? head tired tonight.

Just checked the PCV Hoses, They are all ok, (Almost lost my finger down the hose) ROFL!


Aaron.

[oldtimer]

This sounds like I may be able to help. Let me get it right. On LPG all is OK. On fuel it won't idle properly without hitting the throttle continually. OK if you followed the good advice on how to check for vac leaks & found none, then you have none. So the problem is elswhere. You are right in thinking that carby may be at fault. It appears that you may be running lean. To check this you will need access to the carby throat. Get a little petrol in a seringe and squirt it down the primary throat of the carb or if you prefer disconnect the accelerator pump linkage & manually operate it to squirt fuel in, providing the accelerator pump actually works. Either or, if the engine speeds up momentarily the engine is running lean. There are several caused but the most common 2 are, idle solenoid is malfunctioning or there is a blockage in the idle circuit. How to tell which one? The idle solenoid first. When the ignition is switched on, the solenoid will click. If it doesn't check that power is getting to the solenoid. If there is power, the solenoid is cactus, if no power then trace the electrical fault. If there is power, remove the solenoid and cut or remove the plunger. I can't remember the actual design of how the valve works. It may be a straight plunger which can just be removed and the solenoid refitted or it could have the plunger inside what appears to be a jet. If this is the case twist out the jet & remove the plunger if possible or cut the stem of the plunger. refit the jet & re-install the solenoid. Start engine & see the result. Test the solenoid first once you remove it from the carb before you go snipping it. The purpose of the solenoid is to cut fuel to the idle circuit to avoid engine run-on when switched off. Now if the solenoid proves to be all OK, try removing the mixture screw and giving the idle circuit a shot of compressed air. This probably should be done in conjunction with the idle solenoid removed and hitting the circuit with air through the solenoid hole and the mixture screw hole. Refit everything and adjust the mixture screw for best idle. I have not mentioned a third option yet and that is since it is duel fuel the carby tends to dry out from lack of fuel usage. This can cause gaskets to shrink and form an internal vac leak in the carb. Always run on normal fuel regularly to avoid this. Hope I have helped.
Cheers
Mike

[YNOT]

You're beginning to be a very a very useful person to have around Mike. Why don't you jump onto the introductions page and tell us a bit about yourself.

Tony

[kablea]

Hi oldtimer, :P

thanks for the help mate, just a quick q


It appears that you may be running lean. To check this you will need access to the carby throat. Get a little petrol in a seringe and squirt it down the primary throat of the carb or if you prefer disconnect the accelerator pump linkage & manually operate it to squirt fuel in, providing the accelerator pump actually works. Either or, if the engine speeds up momentarily the engine is running lean.

what will it do if it isn't lean?

Aaron.

[patch697]

Hi oldtimer, :P

thanks for the help mate, just a quick q



what will it do if it isn't lean?

Aaron.

It will start running rough or possibly even stall

[oldtimer]

Well just the opposite. If the mixture is set correctly & you suddenly inject more fuel, the engine will stumble and loose RPM. It may stall depending on how much fuel you chucked down the throat of the carby. About 2ml of fuel injected will be enough for a response.
Cheers
Mike

[kablea]

ok cool thanks guys,

will give it a bash in the morning.

Aaron..

[kablea]

Howdy guys

mixture screw is number 89 in this (http://www.carburetorfactory.com/expvw34.html) diag yeah?



Aaron.

[patch697]

Howdy guys

mixture screw is number 89 in this (http://www.carburetorfactory.com/expvw34.html) diag yeah?



Aaron.

Which diagram????

It may also be called an "idle adjusting screw" do not confuse this with the throttle adjusting screw.

Hope that helps? if not, scan & uplead the diagram your working from so we can help identify it for you.


Cheers
Paul

[kablea]

sorry the hyperlink was atached to "This" lol...
http://www.carburetorfactory.com/expvw34.html

Thanks thats makes alot more sense now :P i got all confused (and scared) when i couldn't find mixture...

Aaron.

[patch697]

sorry the hyperlink was atached to "This" lol...
http://www.carburetorfactory.com/expvw34.html

Thanks thats makes alot more sense now :P i got all confused (and scared) when i couldn't find mixture...

Aaron.

The answer to your question is yes, that is the idle mixture screw.

Do you know anything about retuning Idle mixtures?

[kablea]

A Little Bit, i still a bit nervous to touch it lol.

i'ma thinking i'll see if one of my mates (was a mechanic) will assist me. :) (prob have to bribe with beer lol) he is being dificult atm tho...

but by doing the things above i'm prety sure it is either a internal vac leak that is making it run lean, or the mixture is wrong. or both lol.

Aaron.

[patch697]

If your not confident in what your doing & you can get someone who is then that maybe the better way to go. Even ask your mate to show you how its done cos once shown & explained first hand its something you would be able to do yourself in the future.