Technical poor idle

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Technical poor idle

Robster160

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Joined
May 12, 2021
Messages
8
Hi everybody,

I am hoping someone can help me here.
I have an 850 sport coupe and I am struggling with an idle problem. I thought I had solved it a few times , but each time it comes back.
The car had been running fine, when suddenly it stalled at some lights. I could get it started easily enough but every time I stopped it would stall. After googling the problem it seemed like I had a blocked idle jet and sure enough after cleaning them out it ran well again. But a few weeks later the problem came back. This time I sprayed some carb cleaner at the base to check for an air leak and sure enough every time I sprayed it the revs would rise. So I bought a carb rebuild kit. After the rebuild it ran well (probably better than it ever has). It would even run as low as 300-400 rpm without stalling. I thought the problem was solved an it ran well for about a month. But last weekend the problem came back. Did the spray of carb cleaner test and once again the revs would rise. I tried just giving the bolts holding the carb on a slight tighten, but it didn't make any difference. So I took the carb off again to see if I could see any problems. The base seems flat. But it seems like a lot of the screws / bolts had loosened slightly. I thought maybe I just hadn't tightened them properly, but there are so many that I can't believe I would have missed so many. Would they have just vibrated loose? If so how do I stop it happening again?

Thanks for any help

Rob
 

Lgabb

New member
Joined
Apr 8, 2021
Messages
15
Hi everybody,

I am hoping someone can help me here.
I have an 850 sport coupe and I am struggling with an idle problem. I thought I had solved it a few times , but each time it comes back.
The car had been running fine, when suddenly it stalled at some lights. I could get it started easily enough but every time I stopped it would stall. After googling the problem it seemed like I had a blocked idle jet and sure enough after cleaning them out it ran well again. But a few weeks later the problem came back. This time I sprayed some carb cleaner at the base to check for an air leak and sure enough every time I sprayed it the revs would rise. So I bought a carb rebuild kit. After the rebuild it ran well (probably better than it ever has). It would even run as low as 300-400 rpm without stalling. I thought the problem was solved an it ran well for about a month. But last weekend the problem came back. Did the spray of carb cleaner test and once again the revs would rise. I tried just giving the bolts holding the carb on a slight tighten, but it didn't make any difference. So I took the carb off again to see if I could see any problems. The base seems flat. But it seems like a lot of the screws / bolts had loosened slightly. I thought maybe I just hadn't tightened them properly, but there are so many that I can't believe I would have missed so many. Would they have just vibrated loose? If so how do I stop it happening again?

Thanks for any help

Rob
If the studs are loose on the carb or manifold, a little Loctite will take care of that. I've had problems in the past with debris getting past the idle needle and getting lodged in the passageway to the carb barrel. I had to disassemble the carb and backflush from the tiny ports in the barrel with carb cleaner with the tip of the cleaner tube bent 90 degrees and held against the port.
 

junkycarjunky

New member
Joined
Oct 2, 2020
Messages
9
Hi everybody,

I am hoping someone can help me here.
I have an 850 sport coupe and I am struggling with an idle problem. I thought I had solved it a few times , but each time it comes back.
The car had been running fine, when suddenly it stalled at some lights. I could get it started easily enough but every time I stopped it would stall. After googling the problem it seemed like I had a blocked idle jet and sure enough after cleaning them out it ran well again. But a few weeks later the problem came back. This time I sprayed some carb cleaner at the base to check for an air leak and sure enough every time I sprayed it the revs would rise. So I bought a carb rebuild kit. After the rebuild it ran well (probably better than it ever has). It would even run as low as 300-400 rpm without stalling. I thought the problem was solved an it ran well for about a month. But last weekend the problem came back. Did the spray of carb cleaner test and once again the revs would rise. I tried just giving the bolts holding the carb on a slight tighten, but it didn't make any difference. So I took the carb off again to see if I could see any problems. The base seems flat. But it seems like a lot of the screws / bolts had loosened slightly. I thought maybe I just hadn't tightened them properly, but there are so many that I can't believe I would have missed so many. Would they have just vibrated loose? If so how do I stop it happening again?

Thanks for any help

Rob
Rob. do you have a see through fuel filter? Holley makes a nice one that is glass. I suspect rust in your tank if the bolt issue isn't the problem. I had to after cleaning the carb numerous times, remove the tank, sent it to Tank Renew in Greensburgh, Pa., and after that, not another issue.
 
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Robster160

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Joined
May 12, 2021
Messages
8
Thanks for your replies. I don't think the problem is with the main bolts holding it onto the manifold or rust in the tank. I do have a filter and that is clear, also the carb was actually very clean when I took it apart. It seems to be the other slot headed bolts (they aren't screws are they) coming loose and then causing an air leak. The ones bolting the top to the float bowl. Also the ones on the accelerator pump. Can I use blue Loctite on those?

Thanks again

Rob
 

The Panda Nut

Nutty about Pandas Infected by Panda virus and OPD
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Jan 7, 2012
Messages
3,190
Location
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May be a coil issue? Used to have a Mini that did exactly the same. Coil appeared OK but was not producing enough for a strong spark, Instant failure suggests electrical more than fuel to me.
 
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Robster160

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May 12, 2021
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Thanks for your reply 'The Panda Nut' but it's definitely the carb. It runs great apart from the idle problem.

Rob
 

sizzles

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Jun 8, 2014
Messages
11
Location
West Sussex
Hi Rob, have found that sometimes old carbs suck in air via around the throttle spindle, although perhaps your repair kit included new parts for this? Another avenue might be fuel pump - is enough fuel being pumped at low revs? Good luck with it.
 

The Panda Nut

Nutty about Pandas Infected by Panda virus and OPD
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Messages
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Location
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In repect of bolts loosening. The tiniest amount of thred locker such a one of the appropriate grade of loctite would probably do the trick. New star washers under te crew / bot heads might also help. Onec they are crushed they dont do much. Also even if that filter looks clear, if its 6 months old change it. Any E10 fuel may result in non visible contamination from plastic / rubber parts dissolving. Had a Renault 5 many years back that did much the same every month it would play up. Stripping and cleaning the carb by the roadside took up many an unhappy hour. In the end I fitted two additional in line filters and it eventaully stopped its badness. I hope you get to the bottom of it. Could you post some pics of the carb. Maybe something else might occur.
 
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junkycarjunky

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Oct 2, 2020
Messages
9
Thanks for your replies. I don't think the problem is with the main bolts holding it onto the manifold or rust in the tank. I do have a filter and that is clear, also the carb was actually very clean when I took it apart. It seems to be the other slot headed bolts (they aren't screws are they) coming loose and then causing an air leak. The ones bolting the top to the float bowl. Also the ones on the accelerator pump. Can I use blue Loctite on those?

Thanks again

Rob
Rob. I have never had an issue with the screws in the top of the carb. Make sure they are not stripped and then use the blue loctite. same with accelerator pump. For fun, tank the drain plug out of the bottom of the tank and put a paint strainer in a funnel and see if you get any rusty crap out of it. just to be sure. Good luck. Mike
 
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Robster160

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May 12, 2021
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Thanks for all your replies.

Sizzles, yes it did have a throttle spindle in the rebuild kit

Mike, I think I will leave the fun option of draining the tank as a last resort!

I think I will replace all the spring washers first and see how it goes before using any Loctite.

I will let you know how it goes

Rob
 

timmycm850

Active member
Joined
Feb 28, 2016
Messages
624
Hi all.

How old is the actual fuel. Could be worth adding some 99 octane to bring up the average.

There is a small tank drain but to properly clean it out you need to remove it which means gearbox out.

Loctite any screws and convert all nuts to nylons. Also clean out all the oil vapour tubes under the air filter.

Tjm
 

timmycm850

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Feb 28, 2016
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lastly. Check the opening of the second choke whilst the carb is at idle setting. It should be very slightly open.
 

junkycarjunky

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Oct 2, 2020
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Thanks for all your replies.

Sizzles, yes it did have a throttle spindle in the rebuild kit

Mike, I think I will leave the fun option of draining the tank as a last resort!

I think I will replace all the spring washers first and see how it goes before using any Loctite.

I will let you know how it goes

Rob
Rob. Also very important. Float level must be correct. Mike.
 
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Robster160

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May 12, 2021
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Thanks again for all the replies.

Still not working properly. Fitted new spring washers and used Loctite.

Started it up, and at first it seemed ok when I had it running on the drive. It idled at about 900 rpm. So I took it for a run and all seemed ok for the first 5 miles and then it suddenly died again at idle (this was after a brief 60mph run - is this significant?). Also at one point it backfired slightly through the exhaust (this was just after I came off the accelerator after another brief 60mph run) it then died. Got it home and checked it was bolted down ok. It seemed ok. Tried weakening the mixture and once again it seemed ok. Took it for another run and it did exactly the same as before. Died just after a brief faster run. But this time I struggled a bit to get it started. Needed to put my foot to the floor on the accelerator where as before it would just start. Ran a bit rough as well. The only way I could get it home was to set the idle at 2000rpm. But once I got it home and left it a bit. It would start up and run ok.

Tim,

Fuels new I run the car regularly and always use high octane

Both idle jets are new from the re build kit

I haven't touched the timing

Mike,

I checked the height of the float when I did the re build and it was correct.


Looking back I think if I had just replaced the washers around the idle jets it would have run ok. At one point just after I had checked the idle jet I pulled the rubber washer off and it just crumbled. It was at that point I decided to try the re build kit. As I said it ran really well initially after the re build. I must have done something incorrectly putting the carb back on.


Rob
 

timmycm850

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Feb 28, 2016
Messages
624
hi Rob,

The heat on the hot runs çould be overheating the condenser might be worth putting a new one on it.
Tim
 
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Robster160

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May 12, 2021
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Thanks Tim,

I will get another condenser for it. Although I still think it is something I have done when putting the carb back on. Last time I put a new gasket on, and had to scrape the old one off. I did clean both surfaces, but I wonder whether it hasn't sealed properly and is leaking air at that point now. Do you need to put anything on those gaskets?

Rob
 
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Robster160

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May 12, 2021
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Hi everybody,

Ok I tightened down the base a bit. Fitted new condenser. Re adjusted the mixture screw until It idled nicely. Took it for a run and it ran well again. Got it home and I could smell petrol. Seems to be coming from the accelerator pump. Also when I checked how far out the mixture screw was to run well, it was nearly 3 turns out. When I first had it running well, I think it was only 1 3/4 turns. I did change the accelerator pump diaphragm with the re build kit. Maybe I should take it off again and give it another clean? Or is there another explanation?

thanks again for any help

Rob
 
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Robster160

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May 12, 2021
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Took the accelerator pump off and found I had somehow ripped the diaphragm at the screw hole. Does anyone know whether they are a standard type. The one I got in the kit did seem very thin. although I’m not making an excuse for my own clumsiness.

thanks again

Rob
 
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