1937 ULH starting problem

[shinedogg]

Hey, I have a starting problem, I bubble tested, fixed leaks, checked timing 50 times. She finally started tonight with starting fluid, wouldnt start again. Compression 45 psi. When she ran, she sounded great, so not timing, carb responded good. M55, new everything, float triple checked. Great spark. Can someone suggest something or post a pic of your timer when the timing mark on the flywheel is in the window after the front intake closes?
Thanks, Steve

BTW 37 ULH. Is the compression too low? supposed to be 5.7-1, but the math escapes me.
Steve

[kitabel]

45 is very too low. I'd like to see 75. 45 is with the other plug out, engine warm, throttle full open?
M55 is the wrong carburetor, it's for a smaller engine with higher compression (pre-war EL), but it's probably not your problem.

[govmule84]

Hey, I have a starting problem, I bubble tested, fixed leaks, checked timing 50 times. She finally started tonight with starting fluid, wouldnt start again. Compression 45 psi. When she ran, she sounded great, so not timing, carb responded good. M55, new everything, float triple checked. Great spark. Can someone suggest something or post a pic of your timer when the timing mark on the flywheel is in the window after the front intake closes?
Thanks, Steve

BTW 37 ULH. Is the compression too low? supposed to be 5.7-1, but the math escapes me.
Steve

I usually rough the math out by multiplying the the CR by the atmospheric pressure at your elevation. So if you were at sea level, 14.7 x 5.7 = 83.79, close to that 75 number kitabel recommended.

You are holding your throttle wide open while kicking, right? That will affect readings. Also, you're certain all the valves have enough clearance? That will also affect readings...

[shinedogg]

I wasn't holding the throttle open. I checked the valve clearance and they are good. I will let you all know tonight. Thank you both for responding.

Steve

[Rubone]

M55 is fine on your bike, don't stress over that. Same carb as an M51. Has a small venturi (1-1/16), ULH generally had an 1-1/8 venturi. All the adjustments are in the needles so no issue. Small loss of top speed with better low speed response.

[kitabel]

Same carb as an M51

I'm sorry, just too tired of correcting these mistakes.
Will someone else waste their time here?

[T. Cotten]

Same carb as an M51

I'm sorry, just too tired of correcting these mistakes.
Will someone else waste their time here?

Certainly, Kitabel!

From my perspective, Folks...

No two carbs are alike.

....Cotten

[Tommo]

Some of the comments here are what puts a younger person or new convert to our hobby off and maybe causes them to lose interest.
The question by Steve was to enable him to get a bike to run and as Robbie said it will run on any carb.
Yes there are subtle differences between a M51 and a M55 but those differences will not stop the bike running and in most cases the M55 tuned properly will make the bike run just as efficiently as the original M51.
Spark and fuel make it run and once its established you have both of those you then need to check how they are delivered and if those settings are correct.
Valve timing can be roughly checked when you adjust the tappet clearances as the in and ex valves should be on the rock at TDC on the dead stroke.
You need some compression and with 45psi it should run, won't run to good but it should run.
Steve's question was about timing but he qualified that by saying when it did start it ran just fine so common sense would say there's nothing wrong with the timing, both valve and ignition.
My suggestion to Steve is go back to basics and check everything and if it still wont start then start looking for the oddball faults like for example something earthing out the ignition system when you advance and retard the spark or any of a myriad of other things that could be happening.
If it ran once it won't be much stopping it from running again and surely there must be a AMCA member close by who is prepared to stop by and assist.
Last week I drove close on a thousand miles to assist a fellow vintage motorcyclist with his problems.
Come on, Help this guy don't just pick holes in what he's doing, if I wasn't half a world away I'd try to help the guy out.
.

[exeric]

I have nothing profound to add, Steve as you have had advice from some of the best. I have had some weird problems, however. The few that come to mind are; a bad condenser, points shorting out due to a damaged insulator, unvented gas caps, a sheared pinion gear key, and I'm sure there have been others which I'll post if I can remember them.

[Rubone]

In 1977 when I was building my 44UL I couldn't find a good M51 but ran across an NOS M55. I put it on the bike figuring it would be a temporary fitment while I found the right one. Well, it has run so well over the last 40 years I never got around to changing it. Always a one kick starter when primed or hot, normal fuel economy and nice plug color. Hell, it even still has the OEM cork float which was in it when I acquired it. The bike has lived its life with a sidecar attached and has been ridden at over 11000 ft elevations with a passenger and gear in it on AMCA events. And I am well aware of the subtle internal differences in the two carbs. No worries Tommo, certain "experts" would bitch if I said the sun rises in the east and sets in the west. But then what is the definition of expert...An ex is a has been and a spert (sic) is a drip under pressure...

[kitabel]

Thanks for all the responses.
But, so hard to decide:
Does everyone know exactly how they are different, and what is significant?
Or no one?

Hint: look at both of them on their original installations. See anything different?

[Rubone]

Note that an M55 never had an "original installation", it was a replacement part with updates. And float bowls easily interchange....

[Rubone]

Steve, back to your bike. Is the low speed needle assembled correctly internally? Correct washer under the spring? Throttle plate closing all the way? Gas caps vented?(is fuel flow constant?). What is your points gap? Gap set on high point of cam? Timer fully advanced when checking timing?(fully counterclockwise). No internal short in the timer at full advance?

[shinedogg]

Thank you all for your responses. Spark gap .022, vented caps, still 45 psi with throttle open. strong spark at points and plugs. I'm gonna go through everything once more and I'll let you all know.
Again, thank you.

Steve

[shinedogg]

the presently finiky 37

Phone Pictures 8-22-18 004.jpgPhone Pictures 8-22-18 005.jpg

I thought I'd post a couple of pics of her. Not restored but had to let John Pierce have his way with the original but beat up tin. Everything else looks like it did when I found her, except the muffler (Carls), and the bags (a fella in Europe). She will be my daily ride.

Steve