Problem With Carbs/ignition

[ORB 227 1 Cars]

Well, I have a little problem, I am sure I can fix it with a lot of jiggery pokery, but I would rather take some advice from people who know a little more than me on the subject before I get fully elbow deep in engine bay goo.

 

Basicly, my engine runs and revs on the carbs, it seems to run quite well, but I detect a misfire, narrow it down to pot four and possibly pot three.

 

So, I get the engine running, and the missfire is there, I thought it was the HT on plug 4 so I pull it off while the motor is running, and there is NO change to the engine note so it is obviously providing no power. So, out comes the plug, and a nice spark is found.

 

Hmmm, put it all back together, and start it up again, and the syptoms are the same. If I put the palm of my hand over the trumpet of the carb on pot one, the engine slows up and dies, if I do the same to pot four there is not the same ammount of suction, and nothing happens to the engine running properties.

 

This is the same for pot 3 (crap)

 

So off come the carbs by the rubbers at the manifold, stripped, cleaned and rebuilt with no obvious problems found.

 

Bolted it back up and the symptoms are the same.

 

I have a feelind that there may be an air leak between the head and the manifold, but I am not sure that to cause this effect, it would be more obvious?

 

I tried to spray carb cleaner at the manifold/head to check for an air leak, but I did not get any major signs, infact, I would have thought that what I found was more to do with pot one or two than thrre and four (the latter are the problematic carbs)

 

For info, I am running Megajolt on R1 carbs on a shenpar manifold. Standard MI16 Inlet gasget and all pots are showing similar compression readings.

 

Your thoughts?

 

Can a slight (if any) air leak cause these Issues?

 

Any other clues?

[welshpug 1,661]

have you tried a compression test?

 

edit, must read slower

 

hmm, black art of carbs, too old for me!

Edited October 3, 2009 by welshpug

[Galifrey 1]

Okay

 

there is a good trick you can use to track an air leak. Get a piece of tube, and insert it in your ear, like a stephoscope, use the other end and probe it around the area of concern whilst the engine is running, any leak will become far more apparent.

 

However, I would check the carb float bowls are filling properly, maybe clean the inlet filter, and also check the carb jets if no leak is found.

[ORB 227 1 Cars]

However, I would check the carb float bowls are filling properly, maybe clean the inlet filter, and also check the carb jets if no leak is found.

 

 

I have done all of that, but I am unsure of how to check if the floats are filling properly?

 

If I open the drain screws at the bottom, a lot of fuel runs out of each?

 

Thanks for helping

[Matt Holley 11]

Have you ballanced the carbs? An out of ballance carb can give the rough / miss fire feel to it with out actually having a miss fire, Im not familier with bike carbs though I have dellortos on mine.

[Galifrey 1]

Have you ballanced the carbs? An out of ballance carb can give the rough / miss fire feel to it with out actually having a miss fire, Im not familier with bike carbs though I have dellortos on mine.

 

If fuel is running out, likely they are filling ok.

 

R1 carbs are SU style if memory serves me, ie they work on vacuum raising the slide. it is possible if the seal is damaged the slide isn't rising, and that could also account for the lack of "suck".

 

A butterfly opens at the front, and the vacuum from the engine raises the slide, so I would check to see if they are all opening equally, if they arent then remove the carb top and check for damaged seals (you can carefully stretch the rubber diaphragm to look for pin holes).

 

of course, a manifold air leak will still give the same symptoms, so need to eliminate this first.

[ORB 227 1 Cars]

Thanks Mr Porsche dude.

 

That is pretty much what I thought, thus I wanted someone who knows their stuff to confirm it for me that first so that I was not wasting my time running after problems that are not going to fix the issue!

 

So, tonights job is remove the manifold and try to seal it up properly, and check out the needle rubbers in the top of the carb for seating issues and holes? Although I did remove them the other night, I did not examine them to a high standard.

 

Also, are the standard gasgets the best for sealing up a manifold to the head or would you use a different method? I dont think that face fit will work, but maybe face fit with some kind of sealant?

 

I want to MOT my car before winter sets in, it has been off the road for about 900 years, infact I have never properly had it on the road!

[Galifrey 1]

Thanks Mr Porsche dude.

 

That is pretty much what I thought, thus I wanted someone who knows their stuff to confirm it for me that first so that I was not wasting my time running after problems that are not going to fix the issue!

 

So, tonights job is remove the manifold and try to seal it up properly, and check out the needle rubbers in the top of the carb for seating issues and holes? Although I did remove them the other night, I did not examine them to a high standard.

 

Also, are the standard gasgets the best for sealing up a manifold to the head or would you use a different method? I dont think that face fit will work, but maybe face fit with some kind of sealant?

 

I want to MOT my car before winter sets in, it has been off the road for about 900 years, infact I have never properly had it on the road!

 

I think the standard gaskets are pretty good, they have that rubbery part to aid sealing. Just make sure you clean the surfaces, and if in doubt, use some non setting gasket compound. Hermetite red or gold was always my fave, maybe called hylotye red now.

 

http://www.wilcodirect.co.uk/index.php?mai...roducts_id=4144

 

Good stuff.

[ORB 227 1 Cars]

Oh, bugger!!

 

Well, went through every option last night to try and resolve this.

 

It would appear that after checking again, my HG has indeed failed......

 

 

Getting 150 on pots 1 and 2 but 3 and 4 are shoing about 80 or 90.

 

 

 

Bum.

[Galifrey 1]

Bummer

 

[ORB 227 1 Cars]

Chin up and all that, parts on order, genuine pug HG set for 8 quid. happy days.

 

Will take the motor out tomorrow night and sort it all out this week as there are a few bits that are annoying me anyway.

 

Cars are s*it.

[Galifrey 1]

Chin up and all that, parts on order, genuine pug HG set for 8 quid. happy days.

 

Will take the motor out tomorrow night and sort it all out this week as there are a few bits that are annoying me anyway.

 

Cars are s*it.

 

Like they say, if it has t*ts or tyres, its gonna be trouble!