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GS1000 Cam Timing

  • Thread starter Thread starter sambo
  • Start date Start date
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sambo

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Hi, I have a 78 GS1000 engine I just rebuilt with a big bore 1100 kit for my 77 GS750. I didn't have the service manual for the 1000 just the 750 so I set the cam timing the same as on a 750.

I set the egine at TDC (just using the mark under the ignition cover) and pulled the chain tight in the front and made the arrow point straight up on the exhaust cam and then counted 20 pins and meshed the intake cam arrow with the 20th pin.

Does anyone know if this procedure was correct, or how I can test to see if I have the correct alignment? I can crank the engine and nothing binds (so that's good).

Thanks for your help, Sam
 
cam timing

cam timing

The 2 notches on the end (points side)of the cams should be flush and level with the head. Both pointing out or in depends where the engine is turning
 
backfire through carb?

backfire through carb?

I got it fired up yesterday and started braking it in. I'm getting a little back fire through the lefthand carb (the one that is supposed to be to be hooked to the petcock for vaccum (instead I pluged the carb nipple and just put my tank on prime when I run it).

It backfires when I cruise at a constant speed, or decelerate, but not when I accelerate. It also doesn't do it if I cover the pod airfliter on that carb with my hand.

This is what I have:
1978 GS1000 engine
Fresh big bore (1100) rebuild wiseco 10.25-1
stock carbs
stock exhaust
I haven't sinked the carbs yet or really looked into the timing

Any ideas on what to try would be great, Thanks
 
sync up the carbs and you will probably cure the backfiring problem
 
Well according to all I've read if you run pods without rejetting, you will have issues. Although it would seem something unique is additionally happening with that one carb. Of course you want to do a thorough cleaning/rebuild if you haven't already. Pay close attention to the float height and cleaning the pilot circuit if you're having issues at part-throttle.

I assume you've got the valves adjusted properly since you've rebuilt the engine?

After all that it's important to do a carb sync. In my experience a good vacuum carb sync is not optional and there is no substitute. Even after what I thought was a pretty good bench sync I ended up with a cold pipe at idle and a vacuum sync cleared that right up. The throttle flappers adjustment is so stinkin' precise you've got do to a vacuum sync, especially if you ever want to have any part-throttle consistency.
 
I did rebuild the carbs and jetted up to 110 main and left the pilot jets 15, I ordered a sync tool and it should come today. I adjusted the valves and they should be all correct.

I pulled carb that was giving me trouble and I'm just going to clean it real good again, paying special attention to the pilot circuit (I think you might be right). I let you know how it goes. Thanks for the help
 
Still backfiring

Still backfiring

I cleaned the carb real good, made sure all the passages were open, I even stuck copper wire through all of them to make sure. Then I sync'd the carbs and it still isn't running on the left cylinder and is backfiring through the carb and exhaust. I've been searching the forums and it sounds like the next thing I should do is check my ignition, so that's my project for today and tomorrow. Thanks for all the help.
 
no it wasn't running, but I had the same carbs exhaust and ignition on my old 750 engine and it had the same problem, so I think that means I can narrow my trouble shooting to one of those three things?

I checked my exhaust and there are no blockages and I just thoroughly went through that carb and syncronized them all, so now I'm focusing on the ignition.

Any ideas of tests to do or what to focus on would be great.
 
carb sync

carb sync

Use the WD 40 trick and look for air/vacum leaks. You describe a lean condition.
 
Think intake o-rings or carb boot.Leakage will give exactly the symptoms you describe.

Dink
 
Check all of the above. Also, if you are running the standard pipes you are making about 30% less power than the mods you have made are capable of. The standard pipes do not flow much at all, so will make tuning the carbs very difficult, with quite large mains needed as the airflow is not there. I ran into the same problem when I had to run the bike with standard pipes for a while after it had been tuned for a 4-1. But not all 4-1 pipes are created equal, as I borrowed a spare 4-1 of someone and it was worse than the standard pipes.

A decent pipe on the bike will allow it to breathe, and make tuning far easier, as responses to chnages will be consistent..

Also make sure the plug leads and boots are good condition. And an oil cooler would be nice to make sure the ngine lasts for a while...

I have a 78 GS1000 with a 1080 MTC kit, ported head and 23-53 53-23 cams with 9.8mm lift (standard buckets), 4-1 race style pipe
 
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