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1983 GR650 Bobber

  • Thread starter Thread starter Scudder
  • Start date Start date
S

Scudder

Guest
The gr650 bobber that I've been working on is close to completion. It's a pretty cool looking bike. Bare bones, light weight, and perfect for havin' fun toolin' around the neighborhood.

But... I ended up removing the engine a few times during the process off welding the hardtail and all the other mods that follow because off this. The engine ran prior to all the work. Now it does not.

So far, I can't get it running. It will turn over and back fire very loud, but won't start. I replaced the manifold boots and orings. Dipped and cleaned the carbs. New battery, plugs, caps. I am however running pods, but I purchased and installed a jet kit to accomodate this lean running situation.

I need to get it started to start addressing all the other things that I will most likely run into.

Wondering if the valve adjustment could be way off from removing and installing the motor a few times?

Any suggestions?

Scudder
 
Haven't adjusted the valves yet. That is my next step. I'll check the timing while I'm in there.

Scudder
 
Checked the valves and they are good, as is the timing. However still nothing as far as firing up goes. Every so often I will get a massive backfire with literally a shot of fire coming out the exhauset. I've had problems starting these old bikes before, but nothing like this.

A compression check is next I suppose. The engine, before I dismantled it from the frame several times was always slow to start and smoked badly from time to time. The smoke primarily coming from where the header exhaust attaches on to the head. There was a small gap there when I got the bike. You could literally see flames inside the engine. I put in new exhaust gaskets and I thought that situation was over.

I'm not expert, but does that sound like that could be a compression problem due to carbon build up on the pistons.

scudder
 
One more thing. When I was adjusting the valves, as I rotated the crank shaft, I noticed there was not too much restriction. Even with both plugs in. I've done the same thing with my gs750 and gs850, and they were a bear to turn, even with a plug out. Maybe that is just the difference between a 4 cylinder and a 2 cylinder. I've never worked on a 2 so I have no point of reference.

Scudder
 
Ouch!

Ouch!

So I'm getting 50 psi on the right side and 60 psi on the left. Supposed to have around 130 minimum I believe. Any suggestions?

Hard to believe the bike ran decent, but was always slow to start, before the frame mods. Don't know what I did wrong.

Scudder
 
I'm assuming those are cold PSI readings, since the bike won't start

PSA: One should attend to the mechanical issues first on an old bike, then do the cosmetic changes

Did this bike sit a long time? The rings may be stuck. Shoot some penetrating oil in there and see what happens
 
Thanks Big T. The reason I picked this bike to modify was because it was a pretty strong runner before I started the cosmetic mods etc. I've seen plenty of craigslist bikes that did it the other way around. I didn't want to be one of those guys, but... here I sit with a bike that won't start. :o

The engine was out of the bike sitting for about 3 months, while I did all the welding/mods etc. It did leak quite a bit of oil while sitting out. Never quite determine where the oil came from, so I didn't think anymore about it. Could that have contributed to my situation?

I have been checking the compression with the bike cold. I will spray some penetrating lube in there and see if that works. Wouldn't that be nice?

As I was trying to start it sometimes it would back fire very loud, does that mean anything?

I'm looking forward to figuring this out eventually. Thanks a million.

Scudder
 
Last edited:
Sprayed some lube on the cylinders. They move freely. Compression is still at 60psi and 70psi. It is cold. Don't know how much that affects everything. But I'm only about half the compression that I need, from what I understand.

Scudder
 
comparing compression

comparing compression

The compression on this GR650 bobber has been haunting me a bit and not making sense. I have a gs750 and gs850 that run great and are ridden often... the 850 daily as a commuter. Decided to check compression on both of them. Got the engine warm, checked and both bikes have 90 psi in 2 cylinders. I didn't check all 4 on each, because I got to thinkin' that the compression tester I just purchase might be off. I'm guessing the compression or good runnin' bikes would be higher than 90 psi when warm. The gr650 is putting out 60 and 70 psi cold.

Is my thinking accurate? Could it be the tester? Freight Harbor tester.

Scudder
 
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