Need a spark of hope

[hotrdd]

Have 76 650 with 38 Carbs. And I think I have finally read every carb post on the board and was feeling confident that I was going to get this Bike up and running and tuned properly. I got all of the fittings for a manometer and was preparing to build it but thought I better get the bike idling first. I went out to the shop and set my fuel mix screws at 2 turns out and have set the Boyer electrical ignition previously with a timing light. But after trying for an hour I could get the bike to fire once or twice but not run or get close to idle. The Carbs were recently rebuilt and I did have the bike running after that though very rough and only with lots of choke. How can I even get to the point where I can dial in the Carbs if I can't get it to run.

The engine was rebuilt before I got it and never run. Someone please throw me some help I'm frustrated.

 

[TeeCat]

hotrdd, tell us about your ignition system. I spent weeks chasing an ignition problem through the carbs. If your iggy, particularly, the coil, are stock and original, it is notoriously weak. Also, how is your battery? These bikes will not run well, or at all, with a weak battery, failing coils, or bad plug wires/caps. Do you have fire?

TC

 

[hotrdd]

I'm not sure if I can reply or just vent

I installed a Boyer ignition and have had the bike running rough enough at one point to roughly set the timing. I swapped the battery out for a AMG gel type that has lots of power. After these new parts I rebuilt the Carbs and have just tried to get it started again. Since I've had the bike it's never actually just idled.

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[xjwmx]

The engine was rebuilt before I got it and never run.

What I would do now is a compression test, to see how rebuilt it is. You can borrow a compression tester for free from any parts chain store. If you've done all the carb and ignition stuff by the book it should run if the motor's good. I don't know anything about a Boyer or how to test it, unfortunately. Maybe Boyer does

The good news is if everything's to spec, it will run. It's science. Mostly.

 

[hotrdd]

With lots of choke it did run before I rebuilt the Carbs. Im sure I'm just missing something stupid. Should I just turnout the mix screws a few more turns?

I'm reading the carb guide again now.

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[xjwmx]

Also, I'm puzzled by something. You said it would run roughly at some point. Then it sounds like you changed the mix screw setting and it wouldn't start. Put everything back to the way it was when it was running roughly - and then adjust while it's running and watch the result...


Our posts are overlapping a little bit. When you rebuilt the carbs, did you change anything major, jets, needles? Parts in right order? Go back to how it was.

 

[retiredgentleman]

xjwmx brings up a good point. Compression is basic, so start there to see how things look.

76 carbs normally use a mixture screw set at 1.5 turns as a rough starting point.

I don't know much about Boyer ignition, but I believe they need to be timed with the engine at full advance, yet you say the engine never ran well enough to do that. Your timing could be way out??

 

[thrashin]

just went through an ordeal that resulted in the battery not being charged enough.
try charging it and maybe swapping plug wires around maybe the ign is hooked up wrong?

 

[hotrdd]

I feel like I'm stuck because I can't get the bike run to even set the timing. When I rebuilt the Carbs I didn't do anything major, i just used a rebuild kit from MikesXS. Just a clean and minor replace of old parts. I will do some more testing tomorrow and see what I can discover.

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[xjwmx]

I feel like I'm stuck because I can't get the bike run to even set the timing.

With any igntion, there's some way you're supposed to set it initially. Otherwise even if everything was perfect you still wouldn't be able to run it The manual for your ignition should tell you what to do initially with it.

 

[retiredgentleman]

You said "The Carbs were recently rebuilt and I did have the bike running after that though very rough and only with lots of choke."

Are the float levels set correctly?

That says to me that the carbs are still not cleaned properly. Most likely the pilot circuit is not working fully. Did you remove the pilot and main jet to confirm they are clear? Did you spray carb cleaner from the mixture screw through to the holes in the carb throat?

Read the "carb guide" by grizld1 and 5twins.

 

[hotrdd]

I can get theignition close by lining the white dot up on the Boyer ignition, that didn't work so well last time. I'll set everything back to stock and see where that brings me.

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[hotrdd]

You said "The Carbs were recently rebuilt and I did have the bike running after that though very rough and only with lots of choke."

Are the float levels set correctly?

That says to me that the carbs are still not cleaned properly. Most likely the pilot circuit is not working fully. Did you remove the pilot and main jet to confirm they are clear? Did you spray carb cleaner from the mixture screw through to the holes in the carb throat?

Read the "carb guide" by grizld1 and 5twins.

As far as I'm concerned I took everything out and made sure it was all clear and could get carb cleaner through. I also set the float levels and found one of the Carbs to be way out. I'm sure it's going to be something stupid but it might take me rebuilding these Carbs again to findout

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[5twins]

The rebuild kit from Mike's for your carbs comes with the wrong size jets. If you used them, it probably would be hard to start and/or run badly.

 

[hotrdd]

Wrong jets? With an open intake and exhaust what should I put the old jets back in?

Carb Kits
For the 1976-1977 Models. Each kit contains:
a slide needle clip, pilot & main jets (27.5&135), float needle assembly,
pilot fuel screw with spring, choke plunger, spring & cover gasket, and
float bowl gasket to rebuild (1) OEM Carb.
Order Two.

 

[retiredgentleman]

Yes, there are problems with some of the stuff that Mikesxs sells. I could give you a list, but the carb kits are a prime example.

His carb kits don't always contain the correct jets. 5twins and grizld1 wrote the "Carb Guide", so pay attention to their comments.

76 and 77 carbs use 122.5 main and 25 pilot as stock. The ones you list are for 78 and 79.

Click on "Tech"...............go down to Carb section and read the first post.

 

[hotrdd]

Thanks for the help, I'll swap the old main and pilot jets back in and en see if that helps. Then I need to track down the post that helps me decide what main and pilot to use with my open exhaust and intake. I didn't realize that such a small jet change would cause the bike from even starting.

 

[emzdogz]

you didn't by any chance put octane booster in the gas, did you?

I did this once on my former XS, which had 38's. Had enormous probs with that bike, carbs and timing had been set way off by PO to try and mask carb issue.

At one point in my tuning adventures I put some octane booster in (too much, obviously), and then it just plain would not run. At all.
Had to empty tank.

 

[5twins]

Well, with your open exhaust and intake, the larger jets in the kits shouldn't be too far off the mark. The bike should start and run with them. The 27.5 pilot is probably what you want, the 135 main should be close but may not be exactly the right one. Drop your needles one step with those larger jets.

As I said, none of that should keep the bike from starting. You may have other things wrong in the carbs. Check the float height (25mm) and insure your choke jets are clear. If you can get it running, check timing again. Check valve settings, if too tight, they may be causing a problem.

 

[hotrdd]

When you say drop the needles you mean lower them by raising the retaining ring one notch? They are currently set as per the carb guide. Would that change the ability to even start and idle?

going to start with resetting the timing