Hey guys I've bought a 93 Honda CBR F2 that was being neglected for 2 1/2 years. The guy I bought if off of claims he did work on it but that work has yet to be seen. I've done a carb rebuild on it and synced the carbs the best I can. Now down the the issue I'm having. I can start the bike and it will idle for a few minutes, it will rev up just fine, but after it starts getting warm, according to my vacuum gauges which are attached right after the carbs, I'm getting positive pressure in the 4th bank with kills the bike in seconds. i can get past it a little bit by reving the bike but as soon as i let off and it goes back to idle speed (1.5k) it dies. Can anyone help me out? I think maybe its my carb not set right or maybe one of my valves isn't seating all the way and allowing blow by.

 

Hi and welcome to the forum. I think that doing a compression test might be in order.

 

hey so I got around to testing it I couldn't test C1 cause I can't get the spark plug out, there's nothing to set a socket on. C2 C3 C4 @ 60-70 psi so they are for the most part equal. Now, doesn't that engine usually run around 100psi? would a partly dead battery cause low pressure?

To add more info,
I did have the bike running before I did the carb rebuild. I'm thinking maybe I don't have the piolet jets set to the right spot.... would that cause my issue?
I'm lost
according to another forum someone else was getting 75 psi with a bad gauge so maybe my kit is bad but all of them are even in pressure

 

Yeah, you need a charged and working battery. How fast the engine cranks will affect the compression readings.
It should also be done with all the spark plugs out and throttle wide open and a warmed up engine, ignition OFF.
This isn't always possible, a cold engine will read a bit lower.
If the engine has been sitting a LONG time, then a shot of light oil in the cylinder may be worth it.

Normal compression for an F2 is around 175 psi.
Bikes with a lot of miles, like mine, will be closer to 160 psi.
But as long as they are fairly even across all 4 cylinders, it should run fine.
If you really are around 70 psi, then something isn't right.

 

I had a similar issue with carbs on a 1986 Maxim-X, ended up being the butterfly shaft seals; they seal until the carb bodies get warm, then they become a massive vacuum leak. Honda doesn't sell them, but if you dig around they are available. When I did my F2 carb rebuild I ordered them from a guy in Taiwan.

 

If the engine has been sitting a LONG time, then a shot of light oil in the cylinder may be worth it.
Normal compression for an F2 is around 175 psi.
Bikes with a lot of miles, like mine, will be closer to 160 psi.
But as long as they are fairly even across all 4 cylinders, it should run fine.
If you really are around 70 psi, then something isn't right.[/QUOTE]

A shot of oil is my next step and i ended up finding out my battery was toast so I had to go buy a new one, old one was from 2015.... surprised it still made the bike fire up. It was almost dead too it was having trouble turn over the bike