Cold Cylinder

My 750 combat is cold on the primary side exhaust.
I kick it over & shortly the exhaust gases are warm from the timing side exhaust.
The primary side seems like it never warms up.
The Primary side cylinder and pipe seem to get hot eventually but I think it is surrounding heat transfer.
I have strong spark at the plug.
Adjustment on either side idle speed screw w/ both cylinders firing varies the idle speed.
A finger over the pilot airway at idle at the mouth of the carb again primary side starts to stall cylinder.
If I pull the plug wire off on the primary side the bike continues to run on the timing side cylinder.
If I pull the TS while idling on both cylinders the bike stalls.
It refuses to run on the primary side cylinder solo.
What is going on here?
Thanks,
Marshal

Sounds like your primary side is really not firing for some reason. Mine did that but was obvious by the white wires off the coil (-). that was easy to fix. Try a new plug. Interesting you can adjust the non firing side though, I couldn't do it without the plug firing and a hand over the non firing side carb made no difference, plus it felt like a big single and the throttle response was poor.

Dave
69S

Thank you David,
I had NGK BP7ES installed.
I just purchaed a set of Autoite AP 64's
I'll install and report back.
Any other leads greatly appreciated as well
Marshal

MarshalNorton said:

If I pull the plug wire off on the primary side the bike continues to run on the timing side cylinder.
If I pull the TS while idling on both cylinders the bike stalls.
It refuses to run on the primary side cylinder solo.

Click to expand...

The throttle stops could be out of sync.?
http://www.jba.bc.ca/Bushmans%20Carb%20 ... tml#6SYNCH

The timing side carb throttle stop may be set too high, and the primary side stop set too low? So at idle, the engine is mostly kept running by the timing side cylinder.

Try screwing the primary side throttle stop screw in (thus raising the throttle slide) and see if it has any effect, if the revs rise, turn the timing side carb screw out until the idle revs drop back to normal.


Pulling plug caps off the plugs whilst the engine is running could damage the coils and any electronic ignition.

Swap the plug leads over, i.e. opposite coil running cylinder, see if that changes the symptoms ( doing so will reduce the number of suspect systems ).

Although it sounds more like an idle/pilot valve flow issue.

(edited for more goodera spelling)

Les/Josh,
Thanks I'll try same as suggested.
I hope it is as simple as such.
Marshal

You have to sync your carbs.

JR

Josh Cox said:

Swap the plug leads over, i.e. opposite coil running cylinder, see if that changes the symptoms ( doing so will reduce the number of suspect systems ).

Although it sounds more like an idle/pilot vavle flow issue.

Click to expand...

You can do this if you have long enough spark plug wires and your ignition system has a wasted spark, like most electronic ignitions do.

If the problem moves it's a problem with the ignition, if it doesn't move it's carbs or related to the cylinder/combustion chamber. (maybe low compression on that side?)

-Eric

Are you running twin carbs? I had the same problem on a Triumph triple. Pilot circuit was plugged in one carb so I was getting spark but no fuel and engine was running on 2 cylinders.

Points or electronic ignition?

Thanks for all the responses.
I'm running recently resleeved Amal 932's.
Just done zero miles on same.
Trying to dial in before I take on the road.
I have a points set up still.
Compression feels strong from both cyclinders.
I can stand behind the bike 5' away and feel the exhaust pressure against my hand.
Just one cylinder is cold to touch on the muffler.
I bought a set of AP64 auto lite plugs, I will put in Tuesday and raise the curb idle on
Primary side as Les and others have suggested first. Nothing changes?
Then, I'll dig deeper and start swapping sides w/ plug leads.
Marshal

Marshall, everything points to a carb and not plug electrical issue.

If it was me I would just quickly swap the carbs and fire it up to see if it then fires ok on the left and is cold on the right side to verify the left carb, somehow, is indeed the problem.

As you know, swapping the carbs can be done really very quickly!

Start and then pull plug lead off each jug to see how much each is doing on its own.
First thing I'd suspect is points condenser, then points shorting or mis set, then coil issue, then spark plug or its lead/terminals then carb then valves.
Worth a look in the dark too.

highdesert said:

Marshall, everything points to a carb and not plug electrical issue.

If it was me I would just quickly swap the carbs and fire it up to see if it then fires ok on the left and is cold on the right side to verify the left carb, somehow, is indeed the problem.

As you know, swapping the carbs can be done really very quickly!

Click to expand...

Don't Amals interfere with each other when swapped? I'm sure I've tried that in the past without success.

maylar said:

highdesert said:

Marshall, everything points to a carb and not plug electrical issue.

If it was me I would just quickly swap the carbs and fire it up to see if it then fires ok on the left and is cold on the right side to verify the left carb, somehow, is indeed the problem.

As you know, swapping the carbs can be done really very quickly!

Click to expand...

Don't Amals interfere with each other when swapped? I'm sure I've tried that in the past without success.

Click to expand...

You can definetely swap out all but the body, slide, caps, floats, bowls, jets, needles etc....

Re: Cold Cylinder update

Well problem solved as suggested.
The P/S idle speed screw was set to far out.
Bike would not run on left side cylinder only.
Adjusted and replaced plugs runs on either side now as single.
Have a slight and I mean slight flat spot if the throttle is burpped briskly from idle.
While riding with a load on the engine no problem.
Idling and a brisk brap it gasps.
I can release throttle and idles smoothly.
If I hold the throttle (bike warmed up) after it gasps while on centerstand it will accelerate past flat spot.
Again, from a warmed up and ran motor I get these symptoms.
Cold engine this brisk wrap would stall motor.
Anybody dealt with this before?
Thanks again for the great advise earlier on this post :mrgreen:
Marshal

Not so sure about the new oxygenated/lean fuels but in past a proper tuned Amal would not allow cold starts w/o a tickle or choke till warmed up, let alone take a throttle snap off idle. Sounds like you are almost spot on. In newer bikes and cars they developed accelerator pumps to sprizt fuel in before the air motion got going to suck it up and into chamber.

Not can fine tune float level so 1.5 air pilot turns out gives best idle then diddle timing for best off idle response. Still don't expect any non accelerator assisted carb to stay running if throttle jerked to WOT off idle. Notching spray tube can help get a sooner response but then may have to diddle down the main jet or needle. I will experiment with that someday, right now you are ahead of me.

Re: Cold Cylinder update

MarshalNorton said:

Well problem solved as suggested.
While riding with a load on the engine no problem.
Idling and a brisk brap it gasps.
I can release throttle and idles smoothly.
If I hold the throttle (bike warmed up) after it gasps while on centerstand it will accelerate past flat spot.
Again, from a warmed up and ran motor I get these symptoms.
Cold engine this brisk wrap would stall motor.
Anybody dealt with this before?
Thanks again for the great advise earlier on this post :mrgreen:
Marshal

Click to expand...

I reckon the slide cutaway is too big if the "gasp" is just coming off idle, particualry if the motor is cold. You could try to raise the needles one notch as compensation, but its possibly not the ideal solution, however worth a try.

Mick

Hobot,
I liked your burn out video.
Thanks for the explanation re: amals.
Maybe I'm looking for a solution that doesn't exist.
Runs strong in gear, I'm pleased with outcome of resleeving.
I also glued w/ red adhesive my un cut spray tubes in placed.
The factory peening had gave up the ghost.
Hope you get em together soon.
I'm doing the layshaft bearing next. :shock:
Marshal

Thanks Marshal, I'm of two minds to get a bike working again, but likely can't help myself any more than a moth to flame. Two good shots at deer rumps today if I've been on Peel with paintball machine guns and video. They hunt me down so turn about is fair play. The ones near home turn around in pastures when they hear my motorcycle sounds now : )

The slide and needle suggestions sound like more fun to keep us interested.
But what one considers base line idle another feels is already off idle mixture velocity. Under 1000 rpm throttle snap expected to lag in response or stall, above 1000 should pretty much take throttle as fast as you can snap WOT. There is joy and self esteem if you can improve on that. Best dual Amal response I have as a model was the professionally built dedicated drag race P!!, it idled at steady kettle drum beats 600 rpm, a WOT snap would not stall it but did bog til about 1000 rpm then look out. If I opened just a tad slower there was no bog but slow rve up till 1100-1200 rpm then about instant BATTTT to red line. This beast would pull 4th gear hands off in deep sugar sand ruts making a wake though it yet if I smoothly hit thottle about .3 sec delay would turn into roaring rooster tailing sand dragon up steeps still in 4th and I got too scared to stay on it in the woods.

For battery/lights/no stall risk I set idle to 900-1000 when heading out on road.
When things not completely right I bump that up some to suit till figured out.
Choke and throttle blipping is needed till full warm, then you can set idle by
timing and carb features to suit, not while still 'cold'.

Boyer's tend to instill bog as they don't advance like the points do and definitely can be felt to the spirited riders that 520 size teeth just ain't up for.
Trispark seems best curve so far. in a way thank goodnees Cdo's are almost sail boat like, always something to trim and adjust to max out on current conditions.
Best timing I got on points or Boyer is advance till back fire starts then back off til it just don't. Then I put light on to see where it landed.