Terrible engine noise and backfiring - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 13 (permalink) Old 04-11-2014, 09:51 PM Thread Starter
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Terrible engine noise and backfiring

Hi Guys,

I just bought a '03 VN750 that had been sitting for 5 years. I rebuilt the carbs and petcock and it was running perfect after that, I mean really purring. I took it down the block and when I stopped at an intersection it stalled. When restarted there was a terrible engine noise and the bike backfires. It stalls at idle.

It sounds pretty bad. What do you guys think? Any ideas? It sounds to me like it could be a timing chain problem.

The forum won't let me post a link to the video of it on youtube until I have 5 posts.

it is youtube code 5wEel-EXbYA
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post #2 of 13 (permalink) Old 04-12-2014, 12:09 PM
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Have you tried adjusting your air/fuel screw and the idle adjustment screw on your carbs?

The other engine noise could be your ACCTs. Do a search for "Grambo trick" and try that first. Then look into changing them to MCCTs. There's a sticky thread on that conversion in this same forum.

Last edited by Yankee; 04-12-2014 at 12:21 PM.
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post #3 of 13 (permalink) Old 04-12-2014, 02:11 PM
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Wild problem there, you rebuilt your carby's and fuel tap,rode it down the street,stalled it and now it backfires and snuffs. Weird , did you rev it high, did you engine brake very hard,is your battery cherry?

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post #4 of 13 (permalink) Old 04-12-2014, 05:26 PM Thread Starter
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Thanks for the responses.

I've been working on it and I have more information. Did a compression test, front cyl has 0 psi. Checked cam chain and cam timing, its good. It appears that the left side intake valve is not closing. I can see where the cam follower rests on top of the valve and it doesn't look right, it is off to the side a little bit, and the valve stem is way down in the hole. I guess the engine will have to come out at least because as you guys know there is no room to work in there. I wonder if the valve trashed the piston or vice versa.

Do you think too much oil pressure could pump up the hyd lifter too much and cause this? The bike has 5 year old oil in it, I wanted to at least warm it up before changing it but that could have been a mistake.
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post #5 of 13 (permalink) Old 04-12-2014, 08:37 PM
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When reading post #1, one of my first thoughts was there Oil in the engine....
Kept quiet.... thinking must be other major engine issues...engine pull time !

This will be another interesting thread....pls keep us updated.
Good luck....hope all are minor issues dollar/labor wise
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Last edited by WilliamTech; 04-12-2014 at 10:25 PM.
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post #6 of 13 (permalink) Old 04-12-2014, 11:07 PM
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i have a good connecting rod and piston head from a rear cylinder that i can sell for cheap if you need it and i need to check it but i think i have a front head that is useable let me know if you need it

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post #7 of 13 (permalink) Old 04-17-2014, 01:28 AM Thread Starter
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Here is the bike (most of it)


This is what it looks like now



Front head looking down, notice the crooked rocker arm on the left intake valve? I don't know how that could have happened but my current theory is the baike sat for 5 years and the lash adjuster leaked down, causing enough slop in the rocker arm that it fell off the valve.


Intake cam partially ground down but still usable I think. The valve keepers are off, probably because the rocker was pushing down on the washer and not the valve stem. The amazing thing is the valve moves smoothly, I don't think it's bent at all. The lash adjuster was fully pumped up and same length as one of the other ones. I reused it (after soaking in oil and pumping).



I rigged up my air compressor to the compression tester to fill the cylinder with 100 psi air to hold the valve up tightly. No hissing sound so that is a good sign.


Reinstalling the valve keepers with an improvised tool.


The engine is back together and it has good compression. Next step is reassembling the bike.
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post #8 of 13 (permalink) Old 04-18-2014, 01:36 AM Thread Starter
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I think my engine is going to be OK. The keepers came off the intake valve but the valve doesn't seem to be damaged. Cam has a bit won off one side but it looks usable. I reassembled it without removing the head and now it has good compression. Now I just need to put the engine back in the bike.

I posted a bunch of pictures here yesterday but the post never showed up. Maybe due to the external links.
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post #9 of 13 (permalink) Old 04-20-2014, 11:08 PM Thread Starter
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I found the cause of all the problems. The oil filter was clogged. When I installed the engine the bike started right up and sounded fine but the oil light was on. I had added new oil but no filter change (didn't have one yet and I've never experienced a clogged filter before).

Just a trickle of oil came out of the hole when pressure switch was removed, but when oil filter was removed it spurted oil. With new oil filter the oil light is off and it's running fine and sounds quiet.

With no oil pressure the lash adjuster compressed and allowed the rocker to come off the valve. I'm thankful it did because had it not happened I would have kept going until the engine destroyed itself. The oil light was probably on the first time I rode the bike but it only got about 300 feet before dying. It was the first time riding a VN750 and in bright sunlight, I must have missed the light.
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post #10 of 13 (permalink) Old 04-21-2014, 01:44 AM
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Quote:
Originally Posted by alexkram View Post
I found the cause of all the problems. The oil filter was clogged. When I installed the engine the bike started right up and sounded fine but the oil light was on. I had added new oil but no filter change (didn't have one yet and I've never experienced a clogged filter before).

Just a trickle of oil came out of the hole when pressure switch was removed, but when oil filter was removed it spurted oil. With new oil filter the oil light is off and it's running fine and sounds quiet.

With no oil pressure the lash adjuster compressed and allowed the rocker to come off the valve. I'm thankful it did because had it not happened I would have kept going until the engine destroyed itself. The oil light was probably on the first time I rode the bike but it only got about 300 feet before dying. It was the first time riding a VN750 and in bright sunlight, I must have missed the light.
Cool.glad it wasn't something serious

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