74' S3 running issues

Wilson90 · Mar 22, 2018

Hi folks, I may go on a bit here but I want to try and include everything ( I know how difficult it can be to help without seeing the issue in person)
So,
A few weeks ago I encountered some quite severe issues with the truck, it was intermittently losing power under acceleration not cutting out, but all most as if it dropped back to idle, revs dropped away and it stopped pulling completely, if you let off the throttle and tried again it would come back to life for a time. In addition starting it was quite a task, it would turn over but wouldn't fire. I found to get me out of bother a liberal dose of wd40 in the dizzy would get it trying to fire. I have since changed to a brand new bearmach dizzy, I did the plugs at the same time and set the (weber) carb again. All done and it ran beautifully, never had it running so evenly and at tickover I honestly thought I'd stalled a couple of times. After a bit of a drive I hit traffic and noticed a new noise at idle, a knocking/popping kind of noise, very rhythmic and related to engine speed, I got home and having a scout about i traced the noise to the exhaust (non standard) it sounds like a misfire but the engine was still silky smooth, I went around and took the plug caps off one at a time, but every one made a significant change to the running of the engine. Today I had another look, I found id made a mistake when setting the plug gaps so i went through and fixed that,i reajusted the timing, set the tappets as one was knocking and fired the truck up, again ran very smoothly but still with the popping noise. Out of curiosity I put an old coil back on, lo and behold the popping 'seems' to have gone, but I now have an unstable idle, still smooth but the revs wander slightly at idle, not like a hunting diesel say, but like it drops a few and then picks back up. I'm rather hoping it's some simple cock up I've made, but what's the chances of that ?...
I'm fearful I've burnt a valve out somewhere (leaded head) or knackered a head gasket.
Next things I plan to check/change;
New ht leads
New manifold gasket
Compression test
anyone who has any points to offer, it would be greatly appreciated.

tottot · Mar 22, 2018

Not sure why you should change manifold gasket unless you know it is leaking.Do the compression test. Was the replacement coil duff or the wrong type? Is lift pump working all right? Carb float level correct?

Wilson90 · Mar 22, 2018

It's just something that a friend suggested might be the cause, I don't know that it's definitely at fault, but it's not a bad job to do and it checks another box off the list. My guess is it's just a duff, it's the right sort. I'm not 100% It's cured the issue, I only ran it down the road this evening, will have a bit more of a go tomorrow to see if the popping is definitely gone or not. The pump (I'm assuming were on about the same one, mechanical, cam driven, mounted on the block) I rebuilt last week, seems to pump well using the manual lever, if anything the exhaust smells rich. Not sure on the carb, need to clean it up at some point, I'm not familiar with webbers though, cut my teeth on su's and zeniths

John S · Mar 22, 2018

I’m exhausted (no pun intended) reading this. My humble guess is a fuel/ carb problem. What type of carb do you have ? Backfiring n popping are indicative of blocked idle jets. If it’s a blown exhaust gasket it’d be traceable somewhere. If you have a Weber carb just unscrew the idle jet and give it a good blow through and clean with a tissue. Takes all of two minutes.

Wilson90 · Mar 23, 2018

Ha! How do you think I feel? Sorry, if Its badly written, I never was much cop with English.
It is indeed a Webber, I will give that a shot in the morning, thank you.

Colthebrummie · Mar 23, 2018

You say it is a leaded head, have you been putting the lead additive in your fuel tank? When I first had my series 3, I ran it without the additive and it started running rough, popping and even backfiring. I started putting in the additive and it seems to have cured that problem. The other thing I did was change the ignition points to an electronic module. I was against that idea at first cos I wanted to keep it as original as possible but it made a big difference to the smooth running of the engine and I think it's the best £30 I have spent on it.

Col

Wilson90 · Mar 23, 2018

Hi Col, no i haven't, it's one of those things i allways meant to do but never actually did, I'm looking at changing to electronic ignition soon, the dizzy on it now was just to get me out of the s*** while I sort out some funds

Colthebrummie · Mar 23, 2018

Running untreated petrol will cause the valve seats to burn. It takes quite a while for this to happen but considering the UK switched to unleaded in the 1980's your engine may have covered a heck of a lot of miles since it was last fed leaded petrol. If the valve seat aren't too bad, adding the additive now might reverse the damage to some extent if that what the problem is. The additive isn't expensive, it probably adds about £1.50 to a tank of fuel. Alternatively, you can fit a modified head but that is expensive.

Col

Simon Perks · Mar 23, 2018

Timing chain .... I had the same effect on mine, it was running fine and then exactly what you described in the first post.
It drove me nuts, i did everything i could, valve clearances, ignition, bought a new carb, new points - which i then exchanged for an electronic version.
Sometimes it ticked over fine and drove ok but after a few Km's ... pop pop pop Bang! no power... switch off .. wait a bit and fine ... but then no power and and and.
And then i checked the timing chain because i noticed that after setting the timing it would wander (with a strobe light) ...
It turned out that the teeth on the lower sprocket were so worn that the timing was hardly ever likely to stay.

So i know its a bit of a job, drain oil, drain coolant, strip the water pump but after fitting the new chain, tensioner and sprocket ..
bloody hell what a diference, stable timing, no more back fire and power, like pulling in 3rd up a hill ..

I think it's worth checking - set the timing static and then look to see if the mark wanders.

Good luck mate

Turboman · Mar 23, 2018

Wilson90 said:
Hi folks, I may go on a bit here but I want to try and include everything ( I know how difficult it can be to help without seeing the issue in person)
So,
A few weeks ago I encountered some quite severe issues with the truck, it was intermittently losing power under acceleration not cutting out, but all most as if it dropped back to idle, revs dropped away and it stopped pulling completely, if you let off the throttle and tried again it would come back to life for a time. In addition starting it was quite a task, it would turn over but wouldn't fire. I found to get me out of bother a liberal dose of wd40 in the dizzy would get it trying to fire. I have since changed to a brand new bearmach dizzy, I did the plugs at the same time and set the (weber) carb again. All done and it ran beautifully, never had it running so evenly and at tickover I honestly thought I'd stalled a couple of times. After a bit of a drive I hit traffic and noticed a new noise at idle, a knocking/popping kind of noise, very rhythmic and related to engine speed, I got home and having a scout about i traced the noise to the exhaust (non standard) it sounds like a misfire but the engine was still silky smooth, I went around and took the plug caps off one at a time, but every one made a significant change to the running of the engine. Today I had another look, I found id made a mistake when setting the plug gaps so i went through and fixed that,i reajusted the timing, set the tappets as one was knocking and fired the truck up, again ran very smoothly but still with the popping noise. Out of curiosity I put an old coil back on, lo and behold the popping 'seems' to have gone, but I now have an unstable idle, still smooth but the revs wander slightly at idle, not like a hunting diesel say, but like it drops a few and then picks back up. I'm rather hoping it's some simple cock up I've made, but what's the chances of that ?...
I'm fearful I've burnt a valve out somewhere (leaded head) or knackered a head gasket.
Next things I plan to check/change;
New ht leads
New manifold gasket
Compression test
anyone who has any points to offer, it would be greatly appreciated.

Have you changed the condensor, assuming you have points ignition?

And, as above, timing check, the chains can jump if the sprockets are very worn.

74' S3 running issues

Wilson90

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tottot

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Wilson90

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John S

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Wilson90

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Colthebrummie

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Wilson90

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Colthebrummie

Well-Known Member

Simon Perks

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Turboman

Mab An Gov

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