75 860GT ignition question

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blaine.hale
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Re: 75 860GT ignition question

Post by blaine.hale » Sun Jul 31, 2016 7:50 am

I ordered an ultra sonic cleaner, since I can't access the one I last used. Going to run the carbs through it again and triple check everything.

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Re: 75 860GT ignition question

Post by blaine.hale » Tue Aug 02, 2016 5:58 am

Back in the ultrasonic for the carbs. 1 hour each. Rebuilt and mounted, still no fire.
I'm pretty much out of ideas but I do have a new piece of the puzzle to add to those following along and kindly offering advice.

I was kicking it over last night and noticed an inconsistency in compression. At one point, it just lost all compression and it felt like kicking the motor over with no spark plugs for a good 10+ kicks. Just nothing. It regained a bit of compression and was fine after that. I'm thinking it's time to pull the heads and check the previous owners piston and ring job. Might be some stuck rings?

Lumpy
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Re: 75 860GT ignition question

Post by Lumpy » Tue Aug 02, 2016 3:03 pm

Or sticking valve. Squirt of oil into a cylinder would pinpoint sticking rings. Oil helps seal the gap. I would expect that if you were experiencing lowish compression, that is low compression not no compression you would still get some sign of life. As in an occasional pop/fart/gurgle.
Are your plugs wet and smell of fuel after trying to kick it over?
Have you tried other plugs?
Is the fuel fresh, not 10 years old?

blaine.hale
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Re: 75 860GT ignition question

Post by blaine.hale » Wed Aug 03, 2016 6:05 am

Lumpy wrote:Or sticking valve. Squirt of oil into a cylinder would pinpoint sticking rings. Oil helps seal the gap. I would expect that if you were experiencing lowish compression, that is low compression not no compression you would still get some sign of life. As in an occasional pop/fart/gurgle.
Are your plugs wet and smell of fuel after trying to kick it over?
Have you tried other plugs?
Is the fuel fresh, not 10 years old?
Did the oil trick and got crazy good compression. Would that point to sticking rings? Not a single fart out of it, still.
Haven't tried any other plugs yet. Using new bp7hs.
Fuel is fresh. I'm using a brand auxiliary tank too.

The one thing that could be weird out of your questions is the wet plugs. They don't necessarily smell of fuel or are wet when I pull them after kicking. I'm watching the pumpers inject fuel into the cylinder when I twist the throttle and in a desperate attempt to get some kind of life, I've sprayed started fluid in the cylinders and still got nothing. I was trying to eliminate fuel as the potential issue there.

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Craig in France
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Re: 75 860GT ignition question

Post by Craig in France » Wed Aug 03, 2016 7:39 am

Hi Blaine,

I suspect you know the answer ... :) .

1. If it's sparking, and at the right time ...

2. If it's getting gas, and in the right mix ...

....then there ain't much left :shock: .

Is the compression in both pots weak?

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Re: 75 860GT ignition question

Post by blaine.hale » Wed Aug 03, 2016 7:55 am

Craig in France wrote:Hi Blaine,

I suspect you know the answer ... :) .

1. If it's sparking, and at the right time ...

2. If it's getting gas, and in the right mix ...

....then there ain't much left :shock: .

Is the compression in both pots weak?
Compression in each is identically low at 128/130 on the meter. Looks like I'm pulling the top ends :? :(!

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Re: 75 860GT ignition question

Post by Lumpy » Wed Aug 03, 2016 2:07 pm

If your getting 130 psi compression while kicking it over I would doubt that's what stopping it from starting. You should have some sign of life. If your plugs appear to have some fuel on them then I would guess it's maybe a spark issue. Even if your ignition timing were out you should get a pop or backfire. Unless it's ridiculously out. I have seen a GTS go stone dead when transducers were hooked up back to front. If I read right you have fiddled with cam timing. I would be making absolutely sure you have set it back correctly.

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Re: 75 860GT ignition question

Post by wdietz186 » Wed Aug 03, 2016 5:25 pm

The top ends are pretty simple to take off and inspect, pipe, carb, four bolts and a good yank and it's in you hand. The hard part is dropping it out to do the vert. cyl. New rings will seal more than well enough to let it run, it would probably run with no rings if the piston clearance is close to spec. I would inspect the valve guides for wear. It was very common for both to wear excessively at low mileage. Could be they are worn enough for the valves not to seal reliably. Before all that I would review the manual and make absolutely the cam timing is correct, Pull the right hand cover and check the dots on the bevels AND the distribution gears. You will have to remove the support plate to see all the dots. There are shims on both sides of the distribution gears and they can stick to the plate bearings and the case when pulled so pay attention. The previous owner might have spun the engine marveling at all the pretty parts and gotten everything out of phase. When all that stuff checks out, buy an ignition, even if it works for a while it will crap out eventually and not conveniently. These things I know.

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Craig in France
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Re: 75 860GT ignition question

Post by Craig in France » Thu Aug 04, 2016 12:58 am

I'm going to go back on myself here - sorry!

I agree with Lumpy: 130psi and that engine should run. I say that 'cos my old GT had less than that in the back pot when cold (115), and it always started ...

Bill's right: another timing check (yawn ...) and then I think you're going to be obliged to change the ignition. But more out of frustration than anything else. :( . Sorry!

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Re: 75 860GT ignition question

Post by blaine.hale » Thu Aug 04, 2016 5:10 pm

Well, I went down and swapped the leads for each transducer. One kick and it fired right up! Didn't have a tank on so it rand the fuel out in the bowl and sounded fantastic. Very very smooth and revved great.
After all that, I undid the transducers and rerouted cables through the boots and such to correct them, as I just did a temporary swap earlier. Unfortunately, I can't repeat the same beautiful running again. Kicked and kicked and kicked and it sometimes kicked back on me, but no running =\
What a weird fluke!

I'm going to play with the transducer wiring again this weekend and see if I didn't get all confused when I did the final plug in.

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Craig in France
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Re: 75 860GT ignition question

Post by Craig in France » Thu Aug 04, 2016 11:15 pm

blaine.hale wrote:Well, I went down and swapped the leads for each transducer. One kick and it fired right up!
Excellent! Always like a Happy Ending! Or perhaps not ...
blaine.hale wrote:Unfortunately, I can't repeat the same beautiful running again. Kicked and kicked and kicked and it sometimes kicked back on me, but no running =\. What a weird fluke!
No, it wasn't a 'fluke'! I suggest that what you've done is discovered that there is a shared problem somewhere on the electrical side of the ignition system. So not carbs, not timing, not compression. This is progress!

So it's back to basics: check all connectors etc and hope it's not an electronic component. You sure the engine stop relay isn't playing up?

P.s Please DON'T repeatedly kick Ducrappis! They're not British s**t, you know :shock: ! When set up right, Ducrappis are easy starters. If it doesn't go after 4 or 5 attempts, stop. You'll only exhaust yourself and possibly damage the bike. Find the problem ...

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Re: 75 860GT ignition question

Post by blaine.hale » Fri Aug 05, 2016 9:49 am

Craig in France wrote:
blaine.hale wrote:Well, I went down and swapped the leads for each transducer. One kick and it fired right up!
Excellent! Always like a Happy Ending! Or perhaps not ...
blaine.hale wrote:Unfortunately, I can't repeat the same beautiful running again. Kicked and kicked and kicked and it sometimes kicked back on me, but no running =\. What a weird fluke!
No, it wasn't a 'fluke'! I suggest that what you've done is discovered that there is a shared problem somewhere on the electrical side of the ignition system. So not carbs, not timing, not compression. This is progress!

So it's back to basics: check all connectors etc and hope it's not an electronic component. You sure the engine stop relay isn't playing up?

P.s Please DON'T repeatedly kick Ducrappis! They're not British s**t, you know :shock: ! When set up right, Ducrappis are easy starters. If it doesn't go after 4 or 5 attempts, stop. You'll only exhaust yourself and possibly damage the bike. Find the problem ...

I'm thinking I can find the right configuration up on the transducers to get it started again. There's no way on earth I got it right and it won't start like it did last night.
Side question. I'm not running an engine stop relay right now. I may have the crappy 75 stock one sitting around but I'd like to update it. Is there any modern relay option out there I could pick up? Just seems like a grounding unit, is all.

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Re: 75 860GT ignition question

Post by Lumpy » Fri Aug 05, 2016 7:06 pm

I make them out of bits you can buy at electronics stores. Can list the bits I use if your keen. One I made has worked for years.

blaine.hale
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Re: 75 860GT ignition question

Post by blaine.hale » Fri Aug 12, 2016 5:46 am

Beginning to think that brief running was a fluke. I've tried every wire config on the transducers and haven't been able to reproduce it.
As soon as I get the thing running, I'll post back here.

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Craig in France
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Re: 75 860GT ignition question

Post by Craig in France » Fri Aug 12, 2016 8:02 am

Hi Blaine,

1. Are you still getting consistent sparks on both plugs? If one or other is intermittent, here's a thought (I'm assuming that you've already checked/changed HT leads and caps):

2. Have you checked the resistance of the ignition generator coils and the pick-ups? (They're an integral part of the stator unit if I remember right). The workshop manual gives the following values:
  • Between ground and each of the white, red and green cables you should have no continuity.
    Between the green and white cables, you should get 285 Ohms+/-10% .
    Between the green and red, you're looking for 1000 Ohms +/-30%
3. Really dumb question :-D . You sure the ignition switch isn't playing up?

4. Even dumber question: you SURE you're not running an engine stop relay? I thought the ignition switch worked thru it? If I'm insulting your intelligence here, please feel free to say so ... :doh: . It's been nearly 30 years since I had a 860, so you'll have to forgive me! Maybe I need to look at the wiring diagrams again ...

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