GTL Running problems

[MATTT]

just got it all ready for the mot but need to sort out the rough running

it has a bit of a misfire,im getting some plugs tomorrow,but the main problem is it wont rev properly unless you pull the choke out
with the choke in it hesitates as the push the throttle then on full throttle wont rev too high,sounds like 3000rpm or so

ive cleaned the points and checked the distributor weights are free and the vacuum advance is working , did move the distributor each way a fraction and put it back where it was as ive no timing light here today.The cap and rotor arm are ok

im guessing a partially blocked jet in the carb?
tried squirting the carb cleaner in it no joy
i did have it apart 6 mths ago to check the float and clean the fuel chamber out but not took it apart today


any ideas?

thanks
matt

 

[malcolm]

Sounds like the timing is out. Do you have a strobe light to check the timing? Disconnect the vacuum advance pipe from the carburettor to the distributor and check the ignition timing at idle using a strobe.

 

[MATTT]

set the timing today,read a few other threads 1st,removed the vacuum advance and set the timing mark in the middle of the two static casing marks,then plugged vacuum back in thats ok,seems to rev a little better now but still not perfect
checked inside dizzy for movement when sucking on advance pipe and checked bob weights moving ok
also fitted new gapped plugs and cleaned and checked the points gap ( 0.4mm )

still rough tickover,removed one lead at a time and still hunts up and down and uneven idle so i think the leads are ok,dizzy cap and rotor arnt brand new but clean

just found the other thread about drilling the domed top cover on the carb and checking the gauze chamber filter for blockage so im trying that tomorrow

anything ive missed ?
pesky thing as i want to mot it!

 

[Bertl]

Hi Mattt,
what carb is this? Sounds quite like mine (Solex 32 SEIA) although my GTL isn't as bad as yours.

Robert

 

[MATTT]

HI
Its a zenith 28 i think its called

drilled teh top rivet out this morning and removed the fine filter from inside and screwed a screw inplace of the rivet
also took the top of the carb off and blew all the jets through with carb cleaner
put some forte fuel cleaner int he tank too#

still the same rough idle
darn !
it still seems like an ignition misfire to me
not sure what to do next though,might find a spare Ht lead and change one at a time

 

[malcolm]

The rough idle tends to happen when a cylinder isn't firing. The change in speed at idle is when it does decide to fire for a while. When you've got that it's very often down to the valves in one of the cylinders. Could also be a faulty lead or trouble with the distributor cap.

Not as bad as it sounds - normal if the car hadn't been run for a while - they just need a good run to clean themselves up. But worth checking the rockers to make sure they all have some valve clearance.

Another thing to check would be the three vacuum hoses. One to the carb, one to the rocker cover, and one to the inlet manifold. They meet at a T piece. Any splits in them might cause a weak mixture at idle. Also the one to the manifold should have a restrictor inside it - if it's ever been changed it won't have any more - this can mess up the mixture.

Are you still having problems revving the engine?

 

[MATTT]

still a little hesitant to rev yes
the car wasnt run for 10 yrs so maybe it is a valve not seating like you say

i will check the hoses again,and look for the restrictor,i guess the restrictor is the one to the vacuum advance ? i noticed a brass fitting inline with the hose and wondered what that was

 

[bantamallan]

The restrictoe is in the hose to the manifold, also check for air leaks on the mnifold and carb gaskets, I have had a lot of trouble with these lately, old gaskets just breaking up
Allan

 

[MATTT]

right next installment !

passed the mot although the CO is very lean so i was thinking air leak

sprayed wd40 around inlet manifold all ok,checked small pipe to the manifold the restrictor isnt blocked blew some carb cleaner through it anyway
then tried some cable ties on the end of the pipe just in case
still the same,hunting and stalling and not nice to drive as its a pain

 

[malcolm]

Well done with the MOT. Your car looks smashing.

It's unusual for a GTL to be lean at idle unless something is wrong. That hose to the manifold with the restrictor - it doesn't matter if it's blocked, but if the restrictor was missing it would cause lean running.

It's possible some of the jets inside the carb have become a little bunged up if there's ever been any water in there. I've been known to unscrew them and blow them out with an air line. If you've had the top off the carb and not noticed anything white in there then that probably won't be it.

An obvious cause of lean running would be the mixture screw - previous owners invariably fiddle around with these. Normally they unscrew them to compensate for other problems, but it's possible that a previous owner might have screwed it all the way in thinking it was loose. The setting that works for me is screwed all the way in, then unscrewed by 1.5 turns.

 

[MATTT]

your right it was a jet
just this second got back in
i saw a jet in the float chamber i hadnt cleaned,think its the main jet
just found it was partially blocked up,cleaned it out and now the CO screw is 2 turns out it sounds loads better and revs up freely
still a slight misfire on idle so it had 2 problems,at least its not stalling now so i m going to put a few miles on it and hope its a leaking valve as it was standing so long

 

[malcolm]

Excellent! The main jet is the one at the bottom where you have to remove a brass nut in the end of the float chamber to get a screwdriver to it, but sounds like you've done the job. (Idle jet would have been the thing to sort in any case, and that comes out from the top).

I have some missing at idle on my cars too. Idle speed is steady and the cars run fine, but if you listen to the exhaust there's the occasional phutt noise inbetween the nice firing noises. I've put it down to terrible manifold and silencer design, but haven't really bothered to investigate. With bad valves they tend to run on 3 cylinders occasionally and the gearstick knocks from side to side.

But anyone that can figure out how to get rid of the phutt do shout.

 

[MATTT]

now thats bad news then
mines phutting too !

still a little irratic on idle so i might have to buy myself a colourtune or go for a rolling road tune up.Theres a place about 30 mins away whos classic friendly and can run the car on rollers and find out all sorts of small problems,not been there for a couple of years so i hope its still open

i ll post another thread with all the annoying niggles ive found today on my 1st drive of a 4 ever !

 

[angel]

I have found that the odd phutt on idle is quite normal for any R4...you can get rid of it by adjusting the idle mixture a little richer but it is unnecessary.

 

[pepper]

I was going to mention that BB phuts at idle too, I'd put it down to the fact that the carbs old and could do with a rebuild, it leaks very very slightly so if you leave it for a week it empties the float chamber.

Mind you mines running a Hennessey hot up kit so its a slightly different carb again.

 

[MATTT]

well its not got any better after running about in it all week,still hunting a little with small pops through the exhaust

so i ve been out and blue hylomared the carb base gasket,which made no difference,also sprayed some carb cleaner(as ive run out of easy start) on the inlet manifold/block gasket
this caused the revs to rise slightly so im picking up a new gasket tonight and fitting that hopefully tomorrow

 

[MATTT]

Well quite an easy job,one nut was tight up against the manifold so the socket was hard to get on,otherwise all was pretty easy
its def better and it now runs with the CO mixture screw 2 turns out

also unblocked the pinhole in the brass fitting which is int he vacuum advance pipe,must have missed that somehow before

reset the timing to the middle of the two marks and it idles much better
did find it was def down on power so i drove it and stopped 3 times and advanced the timing a fraction until it just began to pink under low revs full throttle
Then moved it back just a fraction and left it there

It started 1st time this morning which it hasnt done until today,it ticks over much better but still does the occasional "phutt" and misses then returns back to normal
I might just put up with this

Next job probably is the tappetts as its nice and quiet when cold but sounds a bit like a sewing machine when hot
not that terrible but im picky !!

going to put on a few more miles though to let everything settle down