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 Post subject: Cranks and cranks, no start
PostPosted: Wed Aug 09, 2017 12:04 pm 
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Joined: Aug 9, 2017
Motorcycle: 1986 Rebel 450
Rebel: 450
Country: US
State/Province: CT
Hey yall, new to the forum here and looking for some insight. I've got a decent amount of automotive experience but I've recently acquired a *project* bike that has me regularly scratching my head. It's an '86 CMX450C, and it looks like it has had quite of history of PO modifications, including a pipe-only exhaust, in-line fuel filter, cone style air filters, and electrical wiring that makes me want to strip the whole cussed thing down and start from scratch.

I've got a lot of plans for it for the coming winter season, but right now I'm just trying to keep it on the road while the season is upon us. My issue to date is that it doesn't want to start, plain and simple. Symptoms are that it cranks and cranks, to no avail. A few weeks ago, I was on my way home from work when it started to bog down under load. I remembered (albeit too late) that it was low on gas and was planning to gas up on my way home, but since I was closer to home than to the station I took my chances and got as close as I could to home. Thankfully I made it as far as only having to push it up and over one baby hill. So the next morning, I gassed it up and figured it would at least take a while to start, but that it would start with enough tickling of the choke and throttle. It gave a few rumbles and almost wanted to start, but never did. It has now been sitting for about 2 weeks. My initial thought is that, because I don't know the history of the bike and when any work or mods were done, it might be a good idea to start by swapping out the in-line filter. I'm also wondering what a petcock that's in good condition is supposed to look like. Prior to all of this, I did pull the tank and petcock, gave them a good (read:amateur) cleaning, cleaned the carbs and float bowls, and cleaned and re-oiled the air filters. The screen on the petcock seemed to be pretty clear. I did notice that the inside of the tank was looking pretty crappy and had some little crusties rattling around when I shook it that I just couldn't quite get out. If I pull the plugs and drip in a little gas, I can get the cylinders to fire until the fuel is spent, but it never fully starts up.

Sorry for the lengthy background, just trying to provide any relative info. Is it time for a new tank? Petcock? Maybe just a blocked in-line filter? I'm going to pull the plug wires once it's dark out and make sure I'm getting good spark, but I honestly don't think that's the problem. If you have an idea, let me know; I can take pics of anything if that helps. Thanks all!


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 Post subject: Re: Cranks and cranks, no start
PostPosted: Wed Aug 09, 2017 12:37 pm 
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Joined: Feb 23, 2009
Motorcycle: Rebel 250 plus a few others
Rebel: 250
Country: Canada
State/Province: NB
City: Fredericton
From your description it sounds like a fuel feed issue. (you said it would burn off a teaspoon of gas dropped into the cylinders so that indicates ignition is OK) The crusties in the tank will cause problems with clogged screens and filters until you deal with it by thoroughly cleaning the inside and sealing it with a product like Caswells tank liner.
The problem could also be just a lack of a rich mixture to start. On the 250 the correct procedure is open the enrichener (choke) and no throttle at all for starting. I don't know if the 450 is the same or not.

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2004 Honda Rebel 250
2003 BMW K1200GT
2004 BMW R1200GS
1996 Ducati 900SS
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 Post subject: Re: Cranks and cranks, no start
PostPosted: Sat Aug 12, 2017 3:49 am 
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Joined: Jul 4, 2009
Motorcycle: 2016 Honda Rebel
Rebel: 250
Country: USA
State/Province: AZ
City: Chandler
Sounds like somebody seriously messed it up before you got it. If you have good spark, then it is almost certainly a fuel problem. It could be a dirty and/or rusted tank, a bad/plugged up petcock, or it could be inside the carburetors. I have never bought a used bike that did not have dirty carburetors. Even a Rebel I bout with only 1800 miles had a filthy carburetor, likely from a combination of sitting too long with old gas in it, and ethanol gas. Ethanol gas starts to go bad in as little as 6 weeks, and can cause serious damage to fuel tanks and carburetors. If you are getting fuel flow to the carburetors, then it is time to remove and disassemble the carburetors and see what you find in there.

If you intend to keep the pod filters you will need to rejet the carburetors richer, and you will definitely need a proper exhaust system. Straight pipes have no backpressure, and it is impossible to tune a carb to work with no back pressure. It is highly unlikely you would be able to find either a stock system or aftermarket system, though you can look on eBay. If not, then you will need to buy some aftermarket mufflers and find a way to mount them to the header pipes.

_________________
"Obsolete doesn't mean it isn't any good, it just means it isn't made anymore"
"New vehicles move the body,old vehicles move the soul"
"If you understand, no explanation is necessary. If you don't, no explanation is possible"


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 Post subject: Re: Cranks and cranks, no start
PostPosted: Sat Aug 12, 2017 7:29 pm 
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Joined: Nov 29, 2016
Motorcycle: 1999 CMX250C Rebel
Rebel: 250
Country: USA
State/Province: GA
City: Avera
Turn the petcock to OFF.
Disconnect the fuel line after the inline fuel filter.
Turn the petcock to ON, and check that you have a full stream of fuel flowing.
Turn the petcock to RES, and again check that you have a full stream of fuel flowing.

If not clean, and/or replace defective parts in the fuel system, i.e., tank, petcock, screen, lines, filter, etc.

If you have plenty of fuel flow, then clean and balance the carbs.


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 Post subject: Re: Cranks and cranks, no start
PostPosted: Tue Aug 22, 2017 8:04 am 
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Joined: Aug 9, 2017
Motorcycle: 1986 Rebel 450
Rebel: 450
Country: US
State/Province: CT
So I pulled the tank, cleaned the lines and petcock, and sealed it up with Caswell's epoxy as Duckster recommended. I ran some gas through it yesterday and it finally fired up. Seems to idle a little smoother too. I'm thinking what had happened was all the sediment in the tank collected at the bottom when I ran low on gas, and that gummed everything up. I'm hoping that a good cleaning and sealing of the tank means I should be good for a while now. Thanks for the replies!


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 Post subject: Re: Cranks and cranks, no start
PostPosted: Tue Aug 22, 2017 9:16 am 
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Joined: Oct 16, 2005
Motorcycle: 2014 CB500XA
Rebel: None
Country: USA
State/Province: AZ
City: Green Valley
Nice to hear a happy ending.

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John, 2014 CB500XA (Daily Rider), 2009 CRF230L (L'il Red Piglet), 1989 NX250 - sold, 2001 Rebel - sold; first bike was a gently used 1958 Matchless G2 (250 thumper)
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