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Discussion Starter #1
85 VN700

Just recently rebuilt motor...replaced crank, rods and cases(using parts from a 2004). I am 95% sure I timed it correctly. The bike starts up immediately idles and runs very well, no backfiring or popping. There maybe a slight decrease in power from before but it may just be my imagination as it's been 2 years since it ran. After riding 15 min especially on the highway the bike overheats.

I did everything to rework the cooling system. New radiator cap, new thermostat, distilled water w/ water wetter and bled the coolant system of all air bubbles. Also wired the radiator fan to run continuously. Bike still over heats. Then I pulled the new plugs that I had installed, all 4 are white....the bike is running lean on both cylinders.

The carbs are exactly the same as they were before the bike blew up. Same mixture screw settings, same jet kit, every thing exactly the same as before and the bike never ran lean. The carbs just sat for 2 years drained of gas off the bike in a box in my garage. So I am 99.9% its not a carb problem.

Can I be 1 tooth off on timing the cams on both cylinders retarding or advancing the timing causing the bike to run as described above(good with a loss of a little power and severely lean overheating the bike).

OR

Would any amount of being off on the timing cause the bike to run terrible or not all.

Please help this is driving me crazy I put a lot of money and time into rebuilding this motor. The bike runs really good it's just running extremely lean and overheating.
 

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I am no expert in this area, but I believe you would immediately notice if the timing was wrong even by one tooth.

Does the top of the radiator get hot indicating that the coolant circulates? I don't remember how the coolant hoses are routed in VN750, but often you can check if the coolant starts to circulate by removing the radiator cap and observing through the neck if anything happens when the engine heats up to normal operating temperature. Just first remove some liquid or it will overflow as it heats up.
 

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Heading to the DARKSIDE!
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What jets do you have in your carbs? Honestly......to me it sounds like you have a major blockage in either your radiator or your engine block. Is your thermostat installed the correct direction? Could your radiator cap bad/weak? I honestly don't understand........With Water Wetter/Distilled Water and Fan running all the time it should be running cool.
 

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Discussion Starter #4 (Edited)
I am no expert in this area, but I believe you would immediately notice if the timing was wrong even by one tooth.

Does the top of the radiator get hot indicating that the coolant circulates? I don't remember how the coolant hoses are routed in VN750, but often you can check if the coolant starts to circulate by removing the radiator cap and observing through the neck if anything happens when the engine heats up to normal operating temperature. Just first remove some liquid or it will overflow as it heats up.
Yes coolant is circulating top of radiator hotter then bottom...used laser thermometer to check.

Bike is running very lean as indicated by all 4 plugs being white....It's not the carbs as the bike running pretty good just hot because of the lean condition...the only thing i can think of is it's out of time....but how is it out of time and running really good just hot?
 

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Discussion Starter #5
What jets do you have in your carbs? Honestly......to me it sounds like you have a major blockage in either your radiator or your engine block. Is your thermostat installed the correct direction? Could your radiator cap bad/weak? I honestly don't understand........With Water Wetter/Distilled Water and Fan running all the time it should be running cool.
me either....on the VN there is only one way you can install the thermostat so it's good....coolant is definitely flowing through the radiator and engine block....

this is absolutely driving me crazy
 

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Running too lean can be a cause of overheating too. Why not enrich the mix and see if the situation improves?
Bronson.
 

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Running too lean can be a cause of overheating too. Why not enrich the mix and see if the situation improves?
Bronson.
X2^^^^^

Have the fuel/air mix screws been unsealed and adjusted out (richer).
That might be enough. Shouldn`t need bigger jets.
 

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'03 VN750 "Rosie"
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85 VN700

Just recently rebuilt motor...replaced crank, rods and cases(using parts from a 2004).
The first thing I can think of is that you rebuilt a 700cc motor with parts from a 750. I guess they fit or you couldn't have gotten it back together and running, but is there a chance that the timing marks are slightly different between the two? Longer rods? Slightly different spacing on the crankshaft throws? I'm asking this of everybody out there.
 

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Discussion Starter #9
The first thing I can think of is that you rebuilt a 700cc motor with parts from a 750. I guess they fit or you couldn't have gotten it back together and running, but is there a chance that the timing marks are slightly different between the two? Longer rods? Slightly different spacing on the crankshaft throws? I'm asking this of everybody out there.
Everything that I have read says the only difference in the 700 and 750 is the bore dia....cases, crank, and rods are all the same.
 

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Discussion Starter #10
X2^^^^^

Have the fuel/air mix screws been unsealed and adjusted out (richer).
That might be enough. Shouldn`t need bigger jets.
Yes....bike has aftermarket cobra exhaust, air pods and Factory stage 3 jet kit....bike was tuned and ran perfect before rebuild...everything is the same now the carbs in theory should need no adjustment....

The major overheating is taken place when i ride the bike on the highway....at these speeds and % throttle the carb slides are probably about 3/4 of the way up...so the main jets are supplying most of the fuel...not sure adjusting the enrichment screws will do anything....as i said the bike starts and idles near perfect...
 

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Discussion Starter #11
What jets do you have in your carbs? Honestly......to me it sounds like you have a major blockage in either your radiator or your engine block. Is your thermostat installed the correct direction? Could your radiator cap bad/weak? I honestly don't understand........With Water Wetter/Distilled Water and Fan running all the time it should be running cool.
NEW radiator cap
NEW thermostat

I made sure all the water jacket passages were clear before assembling.
 

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1985 VN-700
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Your engine is tighter now with the rebuild. I assume you did the valves as well. I think your fuel mixture is off causing the white plugs. I think my timing is off as well as my bike runs hot as well. More noticeable after I changed the Dampers when I did the stator. The damn thing doesnt line up exactly and I thought I was one tooth off as well. But my bike runs rich. Did you set the static timing with a timing light?
 

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Yes....bike has aftermarket cobra exhaust, air pods and Factory stage 3 jet kit....bike was tuned and ran perfect before rebuild...everything is the same now the carbs in theory should need no adjustment....

The major overheating is taken place when i ride the bike on the highway....at these speeds and % throttle the carb slides are probably about 3/4 of the way up...so the main jets are supplying most of the fuel...not sure adjusting the enrichment screws will do anything....as i said the bike starts and idles near perfect...
I`m out of ideas. I am curious about the " Factory stage 3 jet kit" however. I have been on this board for almost three years and this is the first time I have ever heard of it.:confused:
 

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Discussion Starter #14 (Edited)
I`m out of ideas. I am curious about the " Factory stage 3 jet kit" however. I have been on this board for almost three years and this is the first time I have ever heard of it.:confused:
http://www.factorypro.com/Prod_Pages/prodk24.html

Don't loose this link or you will never find it on their site....looks like some dude stuck in the 90's is their webmaster worst site ever can't find anything on it....great jet kit though...
 

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Yes coolant is circulating top of radiator hotter then bottom...used laser thermometer to check.
So, what was the temperature reading of the top of the radiator? Could it be that the engine is not overheating, but the temperature gauge is not reading correctly? If you undo the fan wiring modification and let the fan sensor control the fan, does the fan run continuously (as it does if the engine overheats)?
 

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Discussion Starter #18
So, what was the temperature reading of the top of the radiator? Could it be that the engine is not overheating, but the temperature gauge is not reading correctly? If you undo the fan wiring modification and let the fan sensor control the fan, does the fan run continuously (as it does if the engine overheats)?
Steam in the overflow....white plugs....
 

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All other things being equal, I understand your frustration and reluctance to suspect the carburetors. However, with a fresh rebuild, as L2 noted above, you should have notably higher chamber pressures, with higher pressures come higher temperatures, and with temperature shifts come A/F ratio shifts.

Since you have white plugs, and white plugs lead to holed pistons - start there! Whether it makes sense as to why the plugs are white is kinda irrelavant right now. Either something isn't right inside you main circuit (don't see that you mentioned going through the carb internals...), or you need bigger mains.

Once you have it running well with tan plugs, and if it's still running hot, then chase cooling system bugs. If you can cool it sufficiently to keep it out of the red, but the cylinder temps stay too high, you can still hole a piston and ruin all your hard work...
 

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Discussion Starter #20 (Edited)
All other things being equal, I understand your frustration and reluctance to suspect the carburetors. However, with a fresh rebuild, as L2 noted above, you should have notably higher chamber pressures, with higher pressures come higher temperatures, and with temperature shifts come A/F ratio shifts.

Since you have white plugs, and white plugs lead to holed pistons - start there! Whether it makes sense as to why the plugs are white is kinda irrelavant right now. Either something isn't right inside you main circuit (don't see that you mentioned going through the carb internals...), or you need bigger mains.

Once you have it running well with tan plugs, and if it's still running hot, then chase cooling system bugs. If you can cool it sufficiently to keep it out of the red, but the cylinder temps stay too high, you can still hole a piston and ruin all your hard work...
Reused old pistons and rings with same cylinders...compression should be the same as before....bottom end rebuild only....
 
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