Project bike having issues

1971_AMC_GUY · January 18, 2014, 12:51:46 AM

I bought a 1990 GS500 that had the engine rebuilt and wasn't running. It has 24,718 miles on it currently. had many issues to start with as the previous owner decided to make a bobber. I know the frame petcock has a bad diaphragm and haven't located a replacement yet. When trying to start it it pops loudly out the exhaust pipe. If you hold the throttle wide open no pops but still won't start. I have already been through both carbs and they are clean and set properly. I could really use some advise.

Janx101 · January 18, 2014, 12:55:37 AM

Don't hold the throttle open ... Fresh fuel.. Clean plugs..make sure your fuel is flowing... Full choke ...

... But definitely don't hold the throttle open ...

The rest of the tech stuff I'll leave to the tech boys...

But popping.... Compression issues maybe?

1971_AMC_GUY · January 18, 2014, 01:01:08 AM

Okay if I go full choke and close throttle it backfires badly out the exhaust. Fuel is fresh and plugs are clean.

Janx101 · January 18, 2014, 01:18:40 AM

Hrrrm ... I'm not the one to diagnose this.... If you search up on faulty/stuck/broken valves though? ... This time of day is normally quiet on the forum... Give it an hour or 2 and they should start filtering back on again...

From my very limited engine know how... Backfiring = mixture is really out of whack OR timing is out of whack OR valve train is out of whack? .. I think...

There will be suitably qualified users on soon I reckon... With actual 'engine open' experience...

... And some engineers too...

Old Mechanic · January 18, 2014, 07:16:52 AM

Check compression and cam timing.

regards
Mech

Suzuki Stevo · January 18, 2014, 08:17:28 AM

Plus Juan on the cam timing, possible tight valves

(When I wrenched for a living...a lot of my time was spent undoing previous work from people that thought they knew what they where doing...anything is possible in a situation like yours when buying used)

1971_AMC_GUY · January 18, 2014, 01:18:14 PM

I have verified and adjusted the valve shims to correct clearance, timing marks are dead on. I changed out to a closer exhaust to stock rather than the shorty that the previous owner had installed. Main jets are 2 sizes over stock. Wiring has been closely examined for any damage, none found. One of the carb diaphragm covers is damaged but i sealed it to prevent vacuum leaks until I can find a replacement.

1971_AMC_GUY · January 18, 2014, 03:22:17 PM

Okay so just pulled both plugs and it is only firing when I let off the start button. Possible faulty CDI? Any thoughts?

Suzuki Stevo · January 18, 2014, 03:26:43 PM

Quote from: 1971_AMC_GUY on January 18, 2014, 03:22:17 PM
Okay so just pulled both plugs and it is only firing when I let off the start button. Possible faulty CDI? Any thoughts?

Battery

1971_AMC_GUY · January 18, 2014, 04:30:39 PM

Brand new battery and testing good. Fully charged.

Suzuki Stevo · January 18, 2014, 06:26:23 PM

Quote from: 1971_AMC_GUY on January 18, 2014, 04:30:39 PM
Brand new battery and testing good. Fully charged.

Hummm, sounded like the classic "I have enough voltage to spin the motor, but not enough left to saturate the coils"

1971_AMC_GUY · January 18, 2014, 07:44:27 PM

I went through the whole harness again and reconnected and I did find a bad spark plug. CDI seems to be firing again so as soon as the new plugs get home I will post the results.

1971_AMC_GUY · January 18, 2014, 10:04:44 PM

The old Suzuki lives again. I will post pictures of the beast tomorrow after I take it first my first test ride since I got the bike. Thank you all for your wisdom.

Golly · January 19, 2014, 01:53:44 AM

Had the same issue. New cdi fixed it

Sent from my GT-I9210T using Tapatalk

1971_AMC_GUY · January 19, 2014, 05:46:40 PM

Yeah it looks like my CDI is fried.

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Project bike having issues