Misfire under load GT2 (Weber)

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NebToast
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Misfire under load GT2 (Weber)

Post by NebToast » Sun Jan 06, 2019 1:38 pm

I got my GT2 1992 Weber carved Rocco on the road taxed and insured this week and it's been fun to finally drive. I took it on a long drive yesterday and had to fill up at a Morrison's in a pinch, they only had 95 so I only put half a tank in to get me there and home. The car developed a lumpiness under load (more than 1cm of throttle in gear) and would judder and misfire a bit. I upped the idle speed and limped it home later but towards the end of the journey the oil pressure light would flicker when it misfired (though my instrument electricals are another issue altogether, when warmed up the full beams cause the rev counter to switch off and the oil pressure light to go completely on, also there's a loose male red spade connector in the engine bay that pops out of the loom near the brake servo but with nothing obvious to connect to)

Anyway I limped it home and this morning gave the carb a good blow through with carb cleaner and compressed air. I gave the fuel pipe a blow and heard bubbles so no blockages. The breather pipe was quite creamy and oily at the carb end but not the engine end and the oil cap wasn't creamy. I gave that all a clean then gave the car a quick run without the airbox and all seemed good, it pulled well. I then took it to Tesco's to fill it up with some Momentum 99 and stop by halfrauds for some octane booster just in case. The lumpy running happened again once warm but I'm hoping once the fuel mixes and runs through that might solve the problem.

The other options are mixture and timing, I tuned the carb with my colourtune the other day as it was running a little rich. I was going to check the timing with my strobe light but I couldn't get the green plug out of the gearbox (I tried a bolthead and mole grips but I wasn't sure what size Alan key was needed, whatever size I didn't have it) also I wasn't sure what timing the engine needed as I know the engine can be timed to take lower octane fuel a bit better. There's a new coil and plugs and by my strobe it seems all the leads are getting good spark.

Any ideas what could be wrong or was it just dodgy fuel and I'm being paranoid?



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james butler
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Re: Misfire under load GT2 (Weber)

Post by james butler » Sun Jan 06, 2019 7:47 pm

sounds like dodgy fuel if it ran fine before, i know ive had a batch of dodgy fuel recently.
i wouldnt mess with anything at them moment for this tank of fuel so wait and see if it improves.
tuning wise the colour tune wont really do the weber justice, it needs to be tuned by ear for the best lean idle setting.
its actually pretty easy to do as long as all your other mechanical parts are ok.


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GT_II
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Re: Misfire under load GT2 (Weber)

Post by GT_II » Sun Jan 06, 2019 9:33 pm

The green timing plug needs a 27mm allen key - this one does the job, although a bit pricey.

https://www.ebay.co.uk/itm/160498037634

I found my 92 GT2 was already set up for 95 RON from the factory. I've got a feeling it was compulsory by then for new cars in the UK to be capable of using normal unleaded, which for our mechanically-timed cars meant retarded.



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james butler
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Re: Misfire under load GT2 (Weber)

Post by james butler » Sun Jan 06, 2019 9:48 pm

GT_II wrote:
Sun Jan 06, 2019 9:33 pm
The green timing plug needs a 27mm allen key - this one does the job, although a bit pricey.

https://www.ebay.co.uk/itm/160498037634

I found my 92 GT2 was already set up for 95 RON from the factory. I've got a feeling it was compulsory by then for new cars in the UK to be capable of using normal unleaded, which for our mechanically-timed cars meant retarded.
i would be suprised it was tuned from the factory to run on 95 unless someone had took it to the dealer to change it.
the 1.8 doesnt like running on normal unleaded, i found when i retarded the igntion on mine to try it the engine started running on and was generaly sluggish
if you want to run normal 95 unleaded get a 1.6


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mark1gls
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Re: Misfire under load GT2 (Weber)

Post by mark1gls » Sun Jan 06, 2019 10:02 pm

The carb cars will run fine on normal unleaded petrol, there’s no advantage using super unleaded petrol them, it’s only fuel injection cars which need/run better on super unleaded.

I would run through the petrol you have put in and then fill up with normal unleaded then set the timing to on 95 RON petrol..

How old are the HT leads, dissy cap, rotor arm and spark plugs?

Common problem with Webber carbs needed a restricted fuel return as the petrol is sent back to tank to quickly, you can test by removing the fuel return pipe and blocking the 2 ends, see if that helps.. A welding tip can be pushed into the return fuel pipe to restrict the fuel flow.
Have a search and you should see a few threads on here and Mk1 golf forums on this sort of problem and cure...


The instrument problem is a faulty earth to the cluster, I had the same problem when you put on high beam on the rev counter drops really low, New earth cable salved my problem.

Have a look here on fitting a new earth for the instruments and bulking out the main connection.

https://vwgolfmk1.org.uk/forum/index.ph ... -and-gauge


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GT_II
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Re: Misfire under load GT2 (Weber)

Post by GT_II » Sun Jan 06, 2019 11:18 pm

On the topic of fuel, the instruction manual for mine says minimum 98 RON for both carburettor and fuel injected versions of the 1.8 engine, 91 RON for the 1.6. It warns that if lower RON fuel is used, high engine loading with full throttle or high engine revs can cause engine damage. The sales brochure says 95 RON can be used after modification of ignition timing by the dealer. The Haynes manual says for mine (with EX engine), the ignition needs to be retarded by 4 degrees to run on 95 RON.

When I checked the ignition timing on mine, I found it was already retarded by about this amount, even though the anti-tamper cover on the distributor securing screw was still intact. This led me to suspect that some of the last GT2 cars were set up with the ignition already retarded in the factory. This fits in with a vague memory I have of a government edict that all new cars sold would have to be capable of running on normal 95 RON unleaded fuel, although which year this took effect I don't know.



mark1gls
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Re: Misfire under load GT2 (Weber)

Post by mark1gls » Mon Jan 07, 2019 3:50 pm

You are probably right and I'm wrong, my carb car is a 1.6 Mk1 and that will run on old 91RON 2 star petrol (no longer avaible) so that happy on 95RON normal unleaded....

So don't listen to me regarding which type of fuel to run your car on. :-D


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chopperoli
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Re: Misfire under load GT2 (Weber)

Post by chopperoli » Tue Jan 08, 2019 12:44 pm

Sounds like you went a bit too lean, give it 1/4 or 1/2 turn rich on the idle screw, see if it improves. On a Weber the idle mixture actually covers a good portion of the part throttle running too and has influence across a wide range. Colourtune is pointless IMO



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Re: Misfire under load GT2 (Weber)

Post by NebToast » Tue Jan 08, 2019 2:29 pm

chopperoli wrote:
Tue Jan 08, 2019 12:44 pm
Sounds like you went a bit too lean, give it 1/4 or 1/2 turn rich on the idle screw, see if it improves. On a Weber the idle mixture actually covers a good portion of the part throttle running too and has influence across a wide range. Colourtune is pointless IMO
The poor running happens when hot though, which surely would suggest it's not too lean as the mixture gets richer when hot?



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Re: Misfire under load GT2 (Weber)

Post by chopperoli » Wed Jan 09, 2019 11:06 am

You have to experiment with these things



NebToast
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Re: Misfire under load GT2 (Weber)

Post by NebToast » Sat Jan 12, 2019 7:36 pm

I got hold of a 27mm hex bar to get the plug out and it's stuck fast, pretty burred now. Any tips for how to get the thing out? I've got a replacement on order so don't mind destruction.

I need to check the timing because after a bit of fiddling with the mixture it's still misfiring under load. I might give a full tune to these instructions (http://www.carburetion.com/Weber/adjust.htm) tomorrow without the colourtune to rule that out (which was useful for my pierburg on the polo but obviously Weber's are a different kettle of fish).



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Re: Misfire under load GT2 (Weber)

Post by mark1gls » Sat Jan 12, 2019 8:54 pm

Start soaking it in some Plusgas might help...

https://www.eurocarparts.com/ecp/p/car- ... &0&cc5_857


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james butler
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Re: Misfire under load GT2 (Weber)

Post by james butler » Mon Jan 14, 2019 6:55 am

waterpump pliers on the outside and wiggle it back and forth till it comes loose.
i never bothered putting mine back in (naughty i know)
you need to tweak the carb then drive it to see how it responds then tweak it some more little by little till you get it performing its best.


I dont mind project cars but I HATE SANDING!!!

NebToast
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Re: Misfire under load GT2 (Weber)

Post by NebToast » Mon Feb 11, 2019 4:35 pm

I've been running momentum 99 for a few fill ups now, I've retuned the carb properly put in new plugs and cleaned the dizzy cap contacts. Annoyingly there's still stuttering. It occurs once the car is warm when accelerating hard usually. It's worse after about an hour's driving. I've ordered new HT leads, cap and rotor as it sounds like it might be spark breakdown. Is there anything else worth looking in to?

I've not been able to check the timing as the plug is still stuck fast, I might have to take a hot knife to it. But given no change with high octane fuel I assume that means it was timed up for normal octane in the first place.

Could it be the dizzy condenser, if so can this be replaced without gumming up the timing and does anyone know the part number for an EX carb dizzy condenser, wasn't sure which one from the parts diagrams on OEMEPC



NebToast
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Re: Misfire under load GT2 (Weber)

Post by NebToast » Thu Feb 14, 2019 12:21 pm

I just remembered the car came with a spare TCI ignition unit (https://www.classic-vw.co.uk/ekmps/shop ... 05-1-p.jpg). What does this unit actually do, and could it be causing running problems under load?