Need some tech help from any Monster experts. Just bought a 1995 M900 with 20,0000 miles on it and was told that it needed to be rejetted. Being a bike newbie I accepted that, but a buddy of mine says the problem the bike has is unlikely to be the jets. The problem is that the bike has absolutely no top end in any gear. After about a half throttle turn the bike just doesn't rev any higher and actually backs off alittle. The fuel/oil filter and oil have all been replaced and the originally owner claims that the valves were recently adjusted 1000 miles ago. I'm going to take it in, but I was hoping to get some idea of the problem before hand. Thanks!
Help! Just bought problematic used Monster
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G
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·Your buddy may be clueless. It could very well need to be rejetted. You'll need to look at the plugs, to get an idea if it's running rich or lean. I'd suggest taking it to someone who does know a thing or two about a carb'd monster.
G
Guest
·Hold on a minute, more information is needed first. You don't state whether this bike is stock or not. Are the carbs stock? What mods have been done to it? Stock those things ran just fine so you have to figure out what changed to make it run bad. Let us know what's going on.
Thanks for the help. The bike is stock, but the original owner said that it had aftermarket exhausts which were sold off. The original exhausts were placed back on recently. He also said (after the sale) that he was not sure if the jets were truly the cause. Could misaligned valves cause this kind of problem. (I'm brand spankin' new to bikes so sorry for the newbie questions)
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5,076 Posts
Sounds like a carburator problem to me, but since you're just getting the bike & it has 20,000 miles on it, why not run it thru a full service. Adjust valves, new belts, change fluids, rejet & clean carbs (& don't forget that the needle seats will need to be replaced).
The bike would have been rejetted with aftermarket pipes. Putting stock pipes back on will make it run like crap. I had one like that and it would backfire and snap, crackle, pop.
If you could borrow a pair of pipes from someone, put them on a try it, that would narrow it done. If you plan on leaving on stock pipes get a set of stock carbs from ebay or put a parts wanted ad on this site., Its cheaper than rejetting back.
If you could borrow a pair of pipes from someone, put them on a try it, that would narrow it done. If you plan on leaving on stock pipes get a set of stock carbs from ebay or put a parts wanted ad on this site., Its cheaper than rejetting back.
It does sound like carb to me as well. I think if it were your valves it would just run crappy at all speeds all the time. The previous owner may have jetted it and adjusted the mix (not sure if you can adjust the main jet on stock carbs cause I have FCRs)
I would suggest getting a set of FCR carbs. Go to ca-cycleworks.com there is a wealth of info on them there and the best part is Chris, the owner, will help you get them tuned just right for your bike. If you dont have the money for them just try and fiddle with the stockers to see what happens.
I would suggest getting a set of FCR carbs. Go to ca-cycleworks.com there is a wealth of info on them there and the best part is Chris, the owner, will help you get them tuned just right for your bike. If you dont have the money for them just try and fiddle with the stockers to see what happens.
And my favorite on the older Monsters like that - Don't forget the fuel pump could be on it's last legs. ;D
Do a Search on here for "fuel pump" and for "Vapor lock" and set the Max Age Since Last Post to 365 days. There's been a ton discussed including the cheap rebuild option. Go back the 365 days because the discussions started almost a year ago after my bike died rolling into Bike Week. Set the Number of Responses to at least 100 to get all the threads.
The good news is it's a cheap fix that's worth doing just to rule out other problems.
Do a Search on here for "fuel pump" and for "Vapor lock" and set the Max Age Since Last Post to 365 days. There's been a ton discussed including the cheap rebuild option. Go back the 365 days because the discussions started almost a year ago after my bike died rolling into Bike Week. Set the Number of Responses to at least 100 to get all the threads.
The good news is it's a cheap fix that's worth doing just to rule out other problems.
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3,931 Posts
I found in switching between the straight through Ducati Peformance carbon cans and the original unmodifed cans that I couldn't really tell much difference in power at all. I've done this both with stock airbox and jetting, as well as with open airbox and richer jets. I don't think it is valid to blame it on the pipes.
If the bike is jetted lean, you can block off part of the intake and see if it improves things. When I first rejetted my M900, it actually ran better with one snorkel in and one out than either both in or both out. I eventually went up a main jet size and opened the airbox all the way for near optimal jetting. It's all described in the jetting FAQ on this site.
I happen to have a spare fuel pump as well as the original (jetted) carburetors from my 97 M900. I'm making good deals on whatever parts I still have left.
If the bike is jetted lean, you can block off part of the intake and see if it improves things. When I first rejetted my M900, it actually ran better with one snorkel in and one out than either both in or both out. I eventually went up a main jet size and opened the airbox all the way for near optimal jetting. It's all described in the jetting FAQ on this site.
I happen to have a spare fuel pump as well as the original (jetted) carburetors from my 97 M900. I'm making good deals on whatever parts I still have left.
turn the fuel off and go run it.
If it gets better right before you stall out. Its running rich.
Turn the fuel on. run the bike. Now run it again pull the choke, How does it run? better? Then it was running too lean. No power on top end might point to bad belts. bad belt timing.
Easy to check. pull cam covers off. inspect belts for missing teeth. take a 5mm allen wrench. the should fit snug betweem the timing belt adjuster pulley and the belt.
If the belts loose, Check cam timing. You will see a timing gear bottom of the " v " Thats the "crank to head pully"
There is a mark on that pulley that should line up with mark on the side of the engine case cover. Now that that is lined up.
Check to see if each cam pulley is lined up on each head.
There will be a mark on the cam pully and a mark on the housing that the cam cover bolts too. All 3 pulleys should line up on the marks at the sametime. If they dont, you have to turn the motor 180* and recheck timing marks. If 2 line up and ones like a tooth off. Thats your top end problem.
Is the bike getting a lot of blow by out the crankcase breather?
What brand of spark plug are you using and whats the number on them? "ngk dpr8-ea9" ?
Are the plugs wet?
What city you from?
Do you see any smoke out the pipes? If so what color?
Do you see any color down the pipes? If so what color?
If the bike was running lean........
When was the fuel filter replaced last?
I hope with a little more info we can help you out.
Michael
If it gets better right before you stall out. Its running rich.
Turn the fuel on. run the bike. Now run it again pull the choke, How does it run? better? Then it was running too lean. No power on top end might point to bad belts. bad belt timing.
Easy to check. pull cam covers off. inspect belts for missing teeth. take a 5mm allen wrench. the should fit snug betweem the timing belt adjuster pulley and the belt.
If the belts loose, Check cam timing. You will see a timing gear bottom of the " v " Thats the "crank to head pully"
There is a mark on that pulley that should line up with mark on the side of the engine case cover. Now that that is lined up.
Check to see if each cam pulley is lined up on each head.
There will be a mark on the cam pully and a mark on the housing that the cam cover bolts too. All 3 pulleys should line up on the marks at the sametime. If they dont, you have to turn the motor 180* and recheck timing marks. If 2 line up and ones like a tooth off. Thats your top end problem.
Is the bike getting a lot of blow by out the crankcase breather?
What brand of spark plug are you using and whats the number on them? "ngk dpr8-ea9" ?
Are the plugs wet?
What city you from?
Do you see any smoke out the pipes? If so what color?
Do you see any color down the pipes? If so what color?
If the bike was running lean........
When was the fuel filter replaced last?
I hope with a little more info we can help you out.
Michael
its either fuel or spark related.......
Its not because of Jets to me.... Larger jets would mean that the bike would run like crap at low RPMS but run a bit better at higher rpms...
Sounds like the carbs arent getting enough fuel..... or the ignition cant keep up with the Revs...
As someone mentioned earlier... replace the fuel pump... and check your ignition system... (check your spark plugs first)
Its not because of Jets to me.... Larger jets would mean that the bike would run like crap at low RPMS but run a bit better at higher rpms...
Sounds like the carbs arent getting enough fuel..... or the ignition cant keep up with the Revs...
As someone mentioned earlier... replace the fuel pump... and check your ignition system... (check your spark plugs first)
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