RH cylinder running cool

Hi, all-

Apologies if you saw my other thread on this in another forum; erased it now that I have more info. Could use some insight from the collective, for sure.


Got my G15-CS assembled, started, and run slowly around the block, but found the bike very sluggish and the RH cylinder was running very cool. Pipe was only warm to touch, and the pressure out the exhaust was noticeably less than the LH. Edit: There was also an occasional pop/snap out the RH pipe at idle, which I attributed to unburnt fuel igniting in the pipe, based on the apparent rich condition.

LH plug had clean insulator and sooty ring around the outside. RH plug (cool cylinder) was wet, with dark insulator.



I swapped the plugs; RH cylinder remained the cool one.

I pulled the carbs off. (Monobloc 389, linked by balance tube, RH with the short bowl.) Found nothing unusual in either, or in the balance tube. First time with Amals of any kind, though, so maybe there is something I don't get. Jet blocks are appropriately tight and the gaskets are in place, so I don't think they're the source of any undue richness. All new gaskets, jets, and needles following a re-sleeving. I am currently waiting on the improved brass/viton float needle before reassembling. Float height seemed a bit low so I have put one gasket under the needle seat.

Valve lash checked cold, .006 all around.

Compression test (cheap Harbor Freight model) dry showed 90 both sides. With a little oil on the rings it was 100 on the LH and 110 on the RH. Kind of a relief to see there wasn't a huge variance between them, even if the tester is somewhat inaccurate overall.

Guessing timing could be the only explanation at this point?? If the timing was just off in general, could it cause this left/right discrepancy? Or is it more likely linked to a poorly-made, uneven ring cam on the mag?

Any ideas on how to proceed would be much appreciated.

There are two guys over on the P11 thread reporting rich conditions using their standard carb jetting, I have just got my Atlas cranked up after a top end job and my preliminary tests indicate rich conditions using my stock set up on the carbs. Now you seem to have similar results. It leaves several of us wondering if modern fuel can be at the root ..... don't take that as Gospel, but I am of a mind to start a new thread on this richness related to standard carb jetting issue.

Regarding cool running on one cylinder, etc. If you have a magneto, you MUST do a timing check. You are correct in suspecting the cam ring. See my tutorial on setting up a K2F magneto ..... https://www.accessnorton.com/NortonCommando/setting-up-and-timing-a-k2f-magneto.19685/

Keep us informed.

Slick

Thanks so much. I only saw your guide once I had installed and timed my rebuilt mag per the instructions in Haynes and factory manuals. Wish I'd looked earlier, but all I checked was the literature I had on-hand.

So I installed using a degree wheel per the instructions, and it does fire and run, which makes me think it can't be too far off...but that variance between the cylinders is disconcerting. Plus, the power is so low it's actually hard to get going in first on a slight grade. I did install a 19t sprocket, anticipating largely road riding rather than dirt, but it's far more sluggish than my (admittedly highly-strung) Royal Enfield 535cc single.

Re: jetting, I was planning on looking deeper into the fine-tuning once I got both cylinders to behave the same with the same carb settings.

It would sure be odd if I had an air leak on the LH side that was making it run better than the RH...

AgentX said:

It would sure be odd if I had an air leak on the LH side that was making it run better than the RH...

Click to expand...

Spray WD40 around the carbs and manifold to test for leaks. Your symptoms could be due in part to a leak.

Check the timing on both cam ring ramps .... for the peace of mind if nothing else.

You may be running so rich on one cylinder, that you are running and firing on one jug only, which may explain the sluggishness you report. Try opening the pilot air screw on the right (sooty side) carb. Opening pilot screw admits more air and leans idle mixture.

Report back.

Slick

Just had to edit thread title...it's the RH that's running cool! Sorry for confusion. Hoping to get to put carbs on and try again later today. Thx for the advice.

Can't detect any air leaks.

No issues in the carbs; new needle installed, float moving fine, tickler working, RH (slave) fuel level matches the LH bowl.

Forgive me for being new to a multicylinder bike here...but the truth is that the RH cylinder simply isn't firing. Yanked the plug wire and it made no difference in running. Yet there is an absolutely massive spark from the fresh magneto.

Time to re-time, looks like...

AgentX said:

Can't detect any air leaks.

No issues in the carbs; new needle installed, float moving fine, tickler working, RH (slave) fuel level matches the LH bowl.

Forgive me for being new to a multicylinder bike here...but the truth is that the RH cylinder simply isn't firing. Yanked the plug wire and it made no difference in running. Yet there is an absolutely massive spark from the fresh magneto.

Time to re-time, looks like...

Click to expand...

A very rich mixture will not fire ..... your RH carb may be excessively rich in the pilot circuit. Open the pilot air screw to see if that makes a difference.

If a K2F sparks on one cylinder, it will spark on the other, except if a major flaw in the slip ring, high tension pickup, or plug cap. Doubtful if these conditions exist, so I think your problem is carb related.

Slick

texasSlick said:

A very rich mixture will not fire ..... your RH carb may be excessively rich in the pilot circuit. Open the pilot air screw to see if that makes a difference.

If a K2F sparks on one cylinder, it will spark on the other, except if a major flaw in the slip ring, high tension pickup, or plug cap. Doubtful if these conditions exist, so I think your problem is carb related.

Slick

Click to expand...

Will do. They are new size 20 pilots...how could it be so much significantly richer than the opposite side at the same air screw setting?

AgentX said:

Will do. They are new size 20 pilots...how could it be so much significantly richer than the opposite side at the same air screw setting?

Click to expand...

It can happen. I had a similar condition once, it was a leaky jet block gasket. I note you said your gaskets were new.

Regarding air screw setting: 1 1/2 turns out is the suggested initial setting ..... adjust as necessary from there.

Slick

Just a couple of thoughts, I see you swapped the plugs but did you try swapping the good side plug and high tension lead and then grounding it to see if it will spark if screwed I to the right hand cylinder side of the mag? Conversely, just to rule out the slip ring pick up, you could take the plug and lead from the right side, hook it up to the left cylinder side of the mag, ground it and see if it sparks. Lastly if the preceding show spark to a grounded plug, you could, as a test, drop the needle by raising it a couple of groves on the dead cylinder to lean it out and then see if it runs. Obviously on a properly set up engine both needles should be in the same position but as a test it might at least let you know if mixture is the issue.
(I'm sure you have done this, but are all jets, needles and slides at least matching on both carbs?)

Thanks, guys.

Bike's not located at my place right now so I don't have casual access to it, but I will look into things. Both sides show what I'd consider an extremely fat spark compared to the EI coil with iridium plugs on my Enfield.

Bodger, the carbs definitely have matching, all-new jets and needles. Always good to make sure, and I did so when I pulled them over the weekend.

Re: the air screw, if it was solely the idle jet that was causing the issue, it probably would have started to fire when I was more in the mid-range during my ride, yeah?

If the air screw comes up inconclusive, I think I might see if I can put the LH carb on the dead cylinder and see if it runs that way... Hopefully things marry up and it can be an effective diagnostic. Sound reasonable, or am I missing something?

A few thoughts after re reading the entire thread: (1) the timing may be off enough so that the left cylinder (which may have a perfect mixture or slightly hotter spark) will run but not the right. One "clue " is that even on one cylinder the bike should run well enough to get you home. DAMHIK; (2) there's nothing to lose by replacing both plugs. Could be they are both marginal but a slightly better spark on left cylinder is enough to fire them (they can look fine when grounded to test but perform poorly under compression); and (3) have you taken the float off and shaken it near your ear to check for a leak into the float? This can cause over rich running and make you chase all kinds of other possible causes. Good luck and please let us know how you make out.

Not that it would make that much difference on initial start up, but are you certain about your .006 valve clearance spec? By memory, on the Atlas and on the 650cc bikes it's .006 inlet and .008 exhaust.

AgentX said:

Thanks, guys.

Bike's not located at my place right now so I don't have casual access to it, but I will look into things. Both sides show what I'd consider an extremely fat spark compared to the EI coil with iridium plugs on my Enfield.

Bodger, the carbs definitely have matching, all-new jets and needles. Always good to make sure, and I did so when I pulled them over the weekend.

Re: the air screw, if it was solely the idle jet that was causing the issue, it probably would have started to fire when I was more in the mid-range during my ride, yeah?

If the air screw comes up inconclusive, I think I might see if I can put the LH carb on the dead cylinder and see if it runs that way... Hopefully things marry up and it can be an effective diagnostic. Sound reasonable, or am I missing something?

Click to expand...

My suggestion to turn out the air screw is for the purpose of elucidating the cause of the problem, not necessarily to correct the problem. If we can get an improvement by a simple "leanout", we can assume we are on the right track, and go from there.

I do not see how one can cross switch Monoblocs ... unless you mean to cross switch jet blocks and other internals. A cross switch of internals might give a hint where the problem lies, but the usual suspect is a clogged air passageway in the pilot circuit which (the air passageway) is in the main body.

Required reading for all Amal DIY owners ..... http://www.jba.bc.ca/Bushmans Carb Tuning.html
and, https://www.princeton.edu/ssp/65-cub-data/library/amalbritbike.pdf

more ..... http://amalcarb.co.uk/downloadfiles/amal/Mono_Hints_and_Tips.pdf

Slick

Texas, I'm probably missing something here, but I thought AgentX could not get the right cylinder to fire even when the engine was running at high enough rpms for him to make some progress on the road - presumably on the left cylinder only. At those rpms he would seem to be well beyond the range of the air screw which would mainly affect idling and starting. That's why I suggested, as an experiment, dropping the needle jet to lean the mixture at what would be normal running rpms. Also agree with you, cannot swap the chopped right carb with the left carb - the one that has the float.

Bodger said:

Texas, I'm probably missing something here, but I thought AgentX could not get the right cylinder to fire even when the engine was running at high enough rpms for him to make some progress on the road - presumably on the left cylinder only. At those rpms he would seem to be well beyond the range of the air screw which would mainly affect idling and starting. That's why I suggested, as an experiment, dropping the needle jet to lean the mixture at what would be normal running rpms. Also agree with you, cannot swap the chopped right carb with the left carb - the one that has the float.

Click to expand...

In general, I agree with the above. However, my experience with a leaky jet block gasket had me running on one cylinder over the full rpm range, at least to 5K rpm which was about the max I could get on one cylinder.

In another thread on this Forum, an OP had us all pondering what ignition problem could be causing his running on one cylinder over the entire rpm range (EI and coils). The OP then posted something that triggered me to suggest he should look to his pilot circuit, in this case the carbs were Concentrics. Another guy chimed in and said he once had a pilot jet come loose. Turned out that was the problem.

AgentX says he has a recently rebuilt magneto, which makes me doubt the problem is mag related (although he may have some timing mismatch, but that should not keep one cylinder dead). Your suggestions on testing the high tension pickup, lead wire, and spark plug cap are good ones, and AgentX should do these for the peace of mind, and to keep, or put us, on the right track. Your suggestion to drop the needle is also a good one ... my suggestion to open the air screw would hopefully provide the same information, but easier to do.

As I write this, my Atlas is running rich after a recent top end job. My carb setup is as original, except I replaced the needle jets ([HASHTAG]#106[/HASHTAG]) with new [HASHTAG]#106[/HASHTAG]. I have not yet the time to pursue this issue further. P400 over on the P11 Thread has found newly made Amal jets for his carbs are different than originals. Perhaps (perhaps means it is purely conjecture) this is the case for other Amal jets. One more thing to keep in mind.

I am confident, between the two of us, with good feedback from AgentX, we will resolve this issue.

Slick

All very interesting. I didn't think about a loose pilot jet. That would certainly wreak havoc with the mixture. As as a final thought about AgentX's problems, even if the bike is over fueling at low to mid rpms, if the main jet is more or less correct the bike should run on the affected cylinder on large throttle openings. For example, if the float is full of gas and therefore not metering at all, the bike should still run on large throttle openings where the only metering is from the main jet. (This is not theory but experience). I have a single carb atlas that runs rich on one side. I just replaced a very worn cam ring thinking the rich symptoms were the result of slightly uneven timing. Also returned all jetting to stock - the PO was running a larger main and leaner needle jet. I know it's sloppy logic to make so many changes at once but I'm curious to see the result.

@Bodger reply #18

One would intuitively think an over rich condition would go away at high revs, but mine did not when my jet block gasket (call out 27, 376/074 on a monobloc parts diagram) was leaking.

Prompted by my last post, I went to the Atlas and pulled the main jet holder, then the needle jet. Lo and behold, the new [HASHTAG]#106[/HASHTAG] needle jet does NOT have the bleed holes as in my originals. John Healy states that ".... removing, or making it (the bleed hole) smaller, increases the fuel flow" Seems like that will solve my rich issue, i.e. my old needle jets go back in. The main point is .... new jets, even if the numbers are the same, may have differences that upset the original carb setup. As I stated in my post #17 above, "one more thing to keep in mind".

Agreed! We should not make too many changes at once. AgentX may have some magneto timing issues, but we need to resolve why he is "single cylindering" before addressing any timing mismatch.

Slick

Thanks all for the continued assistance. I don't have the bike at the apartment where I live but I will report back. I realize the air screw check was intended as a diagnostic and will do so asap.

Re: swapping carbs, my LH carb has the float and the cylinder is firing. That's why I hoped I might be able to put it on the RH cyl (stopping up the disconnected balance tube) and see if it fires that way. I know I mixed up my thread title initially and it likely confused the issue.

I will also recheck for loose jets and obstructions in the carb passages while they are off.

Might be next weekend before I have the bike in hand again, though.