flat spot between 3-4,000 RPM 1987 1.8 GTI CAB
Posted
#1622228
(In Topic #222041)
Newbie
hi guys, new to using this forum as i normally use the fb site but thought id give this ago so apologies if ive done anything wrong. so i have a 1987 mk1 cab 1.8 gti which is running pretty well but i have an an annoying flat spot where it really bogs down if im accelerating throttle fully open between 3-4,000 rpm,it will do it more when hot and not so bad when cold,its almost like fuel starvation?! all the usual things have been changed, coil plugs leads,rotor,new fule pump and pick up pump, could it be a sensor of some sort??? ive checked timing when replacing the cambelt and thats all good too. you can back off the throttle and its fine its just when you try and open it up it bogs down (REALLY ANNOYING) but once over 4,000 rpm it flys. ANY HELP would be fantastic. thanks scott
Posted
Local Hero
What is the CO reading from the last MOT?
Have a read up/search on the WUR, (warm up regulator) as this controls the fuel pressure.
Have a read up/search on the WUR, (warm up regulator) as this controls the fuel pressure.
Last edit: by mark1gls
1988 Mk1 Golf GTi Cabriolet 1.8cc DX, K-jet. Daily drive. 317,000 miles and counting
1978 Mk1 Scirocco GLS 1.6cc FR, Webber carb. Weekend toy.
1978 Mk1 Scirocco GLS 1.6cc FR, Webber carb. Weekend toy.
Posted
Newbie
adjusted the CO to what it should be but no i have not read about WUR, where is this located please?mark1gls said
What is the CO reading from the last MOT?
Have a read up/search on the WUR, (warm up regulator) as this controls the fuel pressure.
Posted
Local Hero
The WUR changes the ratio between the plunger and the air flow to compensate for a cold engine. Id imagine if it were WUR related it'd be more likely to be through out the rev range - not just at a specific rpm.
Last edit: by Yomp
Posted
Newbie
any ideas in that case then please? It's got to be fuel related to me…if you back off when it bogs down it clears and you get full throttle again and revs right round, I've ended up learning how to drive it so it doesn't do it but it would be nice to get it right?! Thanks again scottYomp said
The WUR changes the ratio between the plunger and the air flow to compensate for a cold engine. Id imagine if it were WUR related it'd be throught the rev range not just at a specific rpm.
Posted
Local Hero
Is it a new problem or since you had it?
Posted
Local Hero
Sticky plunger or air flap in the metering head maybe? - If you think its fuel related.
Posted
Local Hero
Does it stutter in the flat spot or just die or feel as if its
running evenly but just flat on power?
running evenly but just flat on power?
Posted
Local Hero
Fuel starvation - like a blocked pipe tends to occur under load but if your managing to back off and then rev right through its not a system starvation so to speak.
Posted
Local Hero
I would also check the advance / retard mechanism in the dizzy. If thats playing up you could have flat spots but maybe not so savage as you describe so I'm not convinced with that suggestion! More thinking out loud!
Posted
Local Hero
BTW the WUR is located to the left of the oil filter housing. Has two fuel pipes going to it from the metering head.
Posted
Local Hero
Yomp said
I would also check the advance / retard mechanism in the dizzy. If thats playing up you could have flat spots but maybe not so savage as you describe so I'm not convinced with that suggestion! More thinking out loud!
The braided rubber hose connecting the vacuum hoses is the common problem as the rubber goes hard over time and leaks air…
1988 Mk1 Golf GTi Cabriolet 1.8cc DX, K-jet. Daily drive. 317,000 miles and counting
1978 Mk1 Scirocco GLS 1.6cc FR, Webber carb. Weekend toy.
1978 Mk1 Scirocco GLS 1.6cc FR, Webber carb. Weekend toy.
Posted
Newbie
so tried it this morning from cold driving it hard (ish) which I don't like doing but had to to double check and it's totally fine when cold pulls like a train right through the Rev range under load…soon as it got up to temperature the hesitation and bogging down happens under load. It's done it since I've purchased it, previous owner said he'd never noticed it (don't believe him) but loved the car so took a chance on it! Any thoughts now we know it's fine when cold? Thanks again for your help allmark1gls said
Yomp said
I would also check the advance / retard mechanism in the dizzy. If thats playing up you could have flat spots but maybe not so savage as you describe so I'm not convinced with that suggestion! More thinking out loud!
The braided rubber hose connecting the vacuum hoses is the common problem as the rubber goes hard over time and leaks air…
Posted
Newbie
it stutters pretty badly between 2500-3500rmp but only when up to temperature if that helps?! If you drive it half throttle like Mrs daisy you'd never know it had an issue but I don't see the fun it that!Yomp said
Does it stutter in the flat spot or just die or feel as if its
running evenly but just flat on power?
Posted
Local Hero
What fuel are you using, normal unleaded or super unleaded?
Does the fuel pump get noisier at all?
Fuel mixture at 2% CO is where you want to be.
Does the fuel pump get noisier at all?
Fuel mixture at 2% CO is where you want to be.
1988 Mk1 Golf GTi Cabriolet 1.8cc DX, K-jet. Daily drive. 317,000 miles and counting
1978 Mk1 Scirocco GLS 1.6cc FR, Webber carb. Weekend toy.
1978 Mk1 Scirocco GLS 1.6cc FR, Webber carb. Weekend toy.
Posted
Settled In
mine ws doing this and advancing the dizzy a little resolved it
Alps 1992 Rivage Green, 1991 Rivage Blue (SOLD), 1986 GTI convertible White (SOLD)
Posted
Newbie
mark1gls said
What fuel are you using, normal unleaded or super unleaded?
Does the fuel pump get noisier at all?
Fuel mixture at 2% CO is where you want to be.
fuel pump stays the same now its been replaced. will check mixture tomorrow lunch thanks and im just using normal unleaded, should i use super unleaded?
Posted
Newbie
Alps said
mine ws doing this and advancing the dizzy a little resolved it
great thanks will try and report thanks
Posted
Local Hero
I tend to ignore factory settings on timing and go by my ear. Head skins, rebores changing comp ratios, differences in modern fuels etc make original settings in accurate. I keep advancing until I hear any form of pinking and then back iit off until the pinking stops completely. Then take a reading with the timing light to see where it is for future reference. May well be worth swapping another WUR to see if it makes a difference as you say it's different between hot and cold running. All our guesses are valid but there are so many things on a k jet that give the same symptoms that without a pressure test it's difficult to say with confidence. It may not even be fuel related at this stage.
Posted
Newbie
Any other things to check guys?? Cars now off the road for winter so I've got time to try things now…I guess WUR is next to try? Just to confirm it bogs down when accelerator is completely open at 2000RPM , if you back off the throttle slightly it's fine it just can't seen to take fully throttle when hot. Thanks in advance
Last edit: by Vezza
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