Rear cylinder suction in exhaust - Star Motorcycle Forums: Star Raider, V-Max, V-Star, Road-Star Forum
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post #1 of 21 (permalink) Old 05-02-2019, 08:22 PM Thread Starter
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Rear cylinder suction in exhaust

Hello all,

Vehicle is a 2007 V-Star 1100 Silverado.

Been a while since I have been active here. Been riding my bike.

Anyways, got my bike out for the season and started it up. Ran great. Ride it to and from work and it ran flawless. We had an 80 degree day and wanted to ride to work. Tried to start up and nothing. After a while, it would backfire.

I pulled the air filter off and tried to crank. Still no fire. I stuck my hand over the front cylinder exhaust pipe and I feel pressure. I do the same thing for the rear cylinder and I get suction.

Gonna check compression tomorrow and see what I get.

Jumped timing, maybe a timing chain break?

Anyone experienced this?

Last edited by Caymen; 05-04-2019 at 09:56 AM. Reason: Adding the bike in question.
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post #2 of 21 (permalink) Old 05-02-2019, 09:12 PM Thread Starter
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I pulled the timing chain cover off of the rear cylinder and the chain is tight and it turns when cranking. Stuck valve? Broken Valve Spring?
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post #3 of 21 (permalink) Old 05-02-2019, 09:18 PM
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Have you checked for sprark and fuel. What do the plugs look like. Any unusual engine noises while cranking? Which bike. If you make a garage with photo and a brief description of bike it really helps us to remember what ride you have or a quick description in your signature line.

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2001 Vstar 1100 Classic (sold), Cobra Slash Cut full exhaust, Dropped 1 inch with lowering links, ORK, 4.5 inch handlebar risers, Ultimate passenger seat, Passenger pegs moved forward 4 inches, Handlebar clock, KN air filter, Viking saddlebags, Additional rear lighting
Loose nut "me" behind the bars
2006 Harley Electra Glide Ultra Classic

https://sites.google.com/site/vstar1100kb/home
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post #4 of 21 (permalink) Old 05-02-2019, 09:40 PM Thread Starter
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Sorry about that. I never thought to mention the bike.

It is a 2007 V-Star 1100 Silverado. Around 10K to 12K miles on it.

Haven't pulled plugs yet. I thought it was crap in the carbs and was rather concerned with no pressure from the rear cylinder. Since an engine is just a modified air pump, I expect pressure to come out the tail pipe. Nothing. Front cylinder...yup, rear...nope.

Will be pulling the wires to check for spark, plugs to check them out, and a compression check.

I had the starter Clutch go out about 5 years ago, so tearing it down doesn't scare me. I was really worried I had a chain break.
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post #5 of 21 (permalink) Old 05-04-2019, 09:54 AM Thread Starter
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Update.

I pulled the plugs. They look OK, but are on the rich side. (got some carbon on them). I do have spark on both cylinders. I put my compression tester and the results don't look good. I am not sure if it is the compression tester itself showing low readings, or if I am not getting a good seal (I am hoping it is not getting a good seal) with only 60 PSI out of both cylinders. So either my compression is fine and I am not getting a good seal or both cylinders are bad. I am thinking the odds of both cylinders going bad is slim...unless timing jumped which I don't think is very likely.

Anyways, I am going to put new plugs in it and see if it will fire with no fuel and a spray of ether. If it fires, the issue is the carbs and I can deal with it.
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post #6 of 21 (permalink) Old 05-04-2019, 10:04 AM
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did you do a wet compression test, with just a tiny bit of oil in the plug hole?

that would point to valves or rings - oil will seal the rings, but not the valves

and did you let it crank thru 5 to 10 strokes till the gauge stopped climbing?
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Last edited by KCW; 05-04-2019 at 10:06 AM.
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post #7 of 21 (permalink) Old 05-04-2019, 10:06 AM
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have to also add, are your sure your battery is 100% ?

because of the electronic ignition you can have an engine that will spin a bit slow, but have zero spark while cranking if the voltage drops below 10V with the starter engaged. This catches a lot of people, because we think if its cranking there should be spark too.

a weak battery will also give you low compression readings.
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post #8 of 21 (permalink) Old 05-04-2019, 07:27 PM Thread Starter
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I got it to fire. I think the carbs need cleaned. I pulled the plugs, and cleaned them. They had carbon on them, so I cleaned with some methanol and a toothbrush. Most of the carbon was removed. Wanted to get new plugs, but nobody had them in stock.

While the plugs were out, I cranked the engine over to clear out the cylinders. Put the cleaned plugs back in and kept the fuel off and shot a little ether in the intake and she fired up and both cylinders were firing.

It is a fuel issue.

I know what caused it. My brother picked up a 1200C Sportster cheap and we worked on it during the winter. Before we tore the Sportster down, we took it for a little ride to check it out and I followed my brother with my bike. When I put it away, I didn't shut the fuel off. Need to clean the carbs.

Well, at least the motor is OK. I am still perplexed that I got suction on the rear cylinder pipe. Will have to check my timing marks. Maybe it is a little off from when I did the starter clutch many years ago, though the bike runs great.

Thanks to all that chimed in. It is appreciated.


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post #9 of 21 (permalink) Old 05-04-2019, 07:46 PM
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carbon on the plugs, wow what would cause that....parking next to a Harley..these bikes like 87 octane.
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post #10 of 21 (permalink) Old 05-04-2019, 07:56 PM Thread Starter
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It is only a 1200C, but man is that bike fast!!! My 1100 gets destroyed by that Sportster. High octane for the Sporty. My 1100, she gets good ole 87 octane.
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