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87 Indy 400 top speed of 50mph

Tuning

 
 
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  #1  
Old 02-11-2013
dc4114dc
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Default 87 Indy 400 top speed of 50mph

Hey new to the site and looking for some help. I have a 87 Indy 400 L/C it won't go above 50 mph and it's really boggy when wide open. sometimes worse than other times. No matter what i do to it. I have cleaned the carbs again and again put it back to factory jets (at least from what i have read) (220 main/35 pilot) it should be rebuilt because the compression is 100 psi and 90 psi the other I'm lost I guess my question is could the low compression cause this? I feel even with those numbers it should run better. What else could cause this?

Thanks for the help
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  #2  
Old 02-11-2013
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First off, what do your sparkplugs look like after a good run? Are they black/dark brown and gooby? Or are they white and ash-ey?

Can you tell if it's a lean bog or a rich bog?

My gut instinct says to give it some new rings, and see what the compression looks like. I could be wrong but your compression looks just a little on the low side.
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  #3  
Old 02-12-2013
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Yes, low compression will cause the problems you are having.
Any PSi below 110 and it's time for at least a refreshed top end.
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  #4  
Old 02-12-2013
dc4114dc
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Plugs are a dark brown. I think I'll pick up a new set of rings and throw them in this weekend. hopefully that will solve my power issues also going to replace all the gas lines just for sh*ts and giggles. what is the proper way of making sure the rings seat before going crazy with it again? i was told a tank of premix and oil injection and not to go over half throttle is this correct?

Last edited by dc4114dc : 02-12-2013 at 08:22 AM.
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  #5  
Old 02-12-2013
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you can give it WOT during break in, but only for a split second at a time. Varying throttle positions constantly is what I usually do for break in, but no extended run time at 3/4 throttle or more.
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  #6  
Old 02-12-2013
dc4114dc
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Ok thanks guys. hopefully get some more snow so I can break the thing in!
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  #7  
Old 02-12-2013
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You get the rings to seat by honing the cylinders. Run premix in the first tank, and wire the oil pump all the way open until it starts smoking like a banshee on the initial test run.
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  #8  
Old 02-12-2013
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while you have it in the garage take the secondary apart and check the buttons
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  #9  
Old 02-13-2013
dc4114dc
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OK, well i took a little video and uploaded it to YouTube the quality is pretty bad because i took it from my phone while trying to drive the most important part anyway is the beginning you can see me punch it and nothing happen at all i know it need a rebuild but i'm sure it has more problems than that because with the same PSI the motor had been doing 76 mph.

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  #10  
Old 02-13-2013
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Clean your carbs.
Do you KNOW that you have good fuel?
check your exhaust for rats nests
clean your clutches
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  #11  
Old 02-13-2013
dc4114dc
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I have done all but clean the clutches I feel like it has to be more than that though
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  #12  
Old 02-13-2013
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Engine sounds OK, clutches are the most neglected part on most sleds, particularly older ones.
Do this test;
remove belt, with a marker draw a straight line on both units from center to outer edge.
Put belt back on and run it. Then see how much of the lines are worn off.
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  #13  
Old 02-13-2013
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That sounds like clutch problems to me. That could be a broken primary spring, or a binding secondary. Even a really bad belt could make it act like that. Hold off on a top end rebuild until you have clutching and carburetion sorted out.
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  #14  
Old 02-14-2013
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I totally agree that its your clutches. 26 year old springs will do that lol. Kinda sounds like the secondary is either broken/worn/not preloaded. I'm sure once you open the secondary you will also find more wrong than that. Best plan of action would be to refresh both clutch springs and make sure you preload the secondary when you put it back in.
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  #15  
Old 02-14-2013
dc4114dc
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figured out it wasn't getting enough gas pulled the fuel pump crud in it and the pulse section was full of watery oil... saw air in the lines when it was running too need to add more gas to see if it's just a low tank or bad lines for that. I agree that the clutches should both be rebuilt but i have no way to pull the primary any tips?
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  #16  
Old 02-14-2013
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All the stuff you can do to the primary without expensive specialty tools can be done in the sled. Put a Quickgrip clamp on the clutch to hold the cover plate on while you remove the cover bolts. Carefully release the clamp because the cover will be spring loaded. Check the fiber bushing in the cover plate, and inspect your spring. Unless you're on the super-tight budget plan, have a new spring on hand to throw in there. If you don't want to buy a new spring, at least inspect the old one. They do break. Make sure all the rollers that the weights hit are free-spinning. Make sure the pins that hold the weights allow the weights to swing freely. Wiggle the weights back and forth to make sure there isn't enough slop to allow the weight to swing off the roller.
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