HELP! Decompression; - Honda TRX Forums: Honda TRX 450R Forum
 
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post #1 of 9 (permalink) Old 05-10-2017, 12:09 PM Thread Starter
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HELP! Decompression;

So I just installed kibble white stainless intake valves and a J.E. 13.5:1 piston. set the decompression to 60psi with compression gauge and the bike fired right up... several times. got it good and warm and then would not start. checked compression and it had jumped to over 90. I took it apart, checked decompression arm, and the adjuster was still locked tight. wondering why it changed so much so fast without coming loose and backing off but I went ahead and reset it to 60psi again and BINGO fired right up, no issues took if for about a 10 minute ride, came back parked it and tried to fire it up again and nothing. it was late and i needed to get out of the shop so i did not check decompression again but i can only assume thats whats up again...... is this normal with new valves and piston? any advise would be greatly appreciated.
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post #2 of 9 (permalink) Old 05-11-2017, 08:51 AM
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Did you cut new seats when you put in the valves? The new valves can wear in a little and need reshimming soon after rebuilding. I guess you checked the valve clearance when you reset the decomp too? Also I would look at the end of the decomp screw and make sure it isn't wearing where it rides on the arm.

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post #3 of 9 (permalink) Old 05-15-2017, 11:07 AM Thread Starter
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Originally Posted by duke416ex View Post
Did you cut new seats when you put in the valves? The new valves can wear in a little and need reshimming soon after rebuilding. I guess you checked the valve clearance when you reset the decomp too? Also I would look at the end of the decomp screw and make sure it isn't wearing where it rides on the arm.
Thanks for the reply. I have rode about 3 hrs since rebuild and need to check clearance, however I did find the problem. I just wasn't setting it in the sweet spot. Set the decomp cold and once warmed up it was giving me too much compression for the electric start. got it good and warm then quickly tore down and set it at 60psi @ w.o.t and now it starts and runs like a charm at any temp! I am however wondering about the excessive engine noise... is that a high compression thing? my crank/rod had ZERO play up and down but it sure makes a louder knock then it did on the stock piston. runs like a stripe ass ape but had a lot of "knock" everyone tells me that its how they are ??
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post #4 of 9 (permalink) Old 05-15-2017, 12:07 PM
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They have some engine noise but shouldn't be a loud knock. What piston did you put in and what fuel are you running?

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post #5 of 9 (permalink) Old 05-15-2017, 12:23 PM Thread Starter
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They have some engine noise but shouldn't be a loud knock. What piston did you put in and what fuel are you running?
I don't know how to describe it. I heard from everyone that i make listen to it that it is normal. to me it sounds like a knock but I' ve always been a 2stroke guy. I am running a J.E. 13.5:1 standard 96mm bore and I am burning 110 Turbo Blue race fuel. It had the same noise with she stock 10:1 but was not quite as loud. if i am wearing a helmet i barely heard it but starting without a helmet and moving it or loading it up i hear it clear and it drives me nuts lol
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post #6 of 9 (permalink) Old 05-16-2017, 09:21 AM
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See if you can upload a video or something, it could be piston slap, rod knock, main bearing, clutch.... a few things basically, some worse than others.

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post #7 of 9 (permalink) Old 05-16-2017, 07:42 PM
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If the crank, rod and piston is tight, mostly around idle it's the main drive gear backlash

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post #8 of 9 (permalink) Old 05-16-2017, 08:35 PM
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how do you set decomp?
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post #9 of 9 (permalink) Old 05-19-2017, 08:43 AM Thread Starter
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how do you set decomp?
I set decompression with a compression gauge. that issue is solved. i am more concerned about the engine noise at this point.

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Originally Posted by gboezio View Post
If the crank, rod and piston is tight, mostly around idle it's the main drive gear backlash
well the 13.5:1 piston is less then 2 weeks old. the fitment was perfect in the cyl, the rod has zero play up and down just a small bit side to side which is normal and in spec. It IS only around idle its louder when warmed up and it does pick up speed with rpm but only to a certain point then you no longer hear it.
I am pretty positive its not piston or rod but my concern is something coming apart in this fresh build and being down again.
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