AboutBill Silver Expertise Need help with vintage Hondas from the 1960s? I am an expert with 250-305cc bikes in particular and most all of the other pre-91 models, in general. I do NOT claim to have a great deal of experience on Gold Wings, Cruisers, ATC/ATVs and dirt bikes.
Experience I have owned/ridden/maintained Honda motorcycles for 35 years. I have written five books on Honda repairs and collecting. I was a service manager for two Honda shops back in the 1980s.
Organizations VJMC (Vintage Japanese Motorcycle Club) of North America
Publications VJMC newsletter, as editor for two years and as contributing editor currently.
Question Hi, I have a 84 honda magna 700. I have just replace the all jets in the float bowl, the floats, and clean/re-seat the diaphrams on all 4 carburetor. I also replace plugs and change oil and air filter. The bike now starts instantly everytime and idles perfect.
The problem is when I open the throttle to 5 k rpm or higher, the bike hesitates and bogs big time. It has plenty of power up to 5k rpm on all gears. I fully open the throttle and it then sometimes sputters and accelerates to high rpms but more often it sputters and DECELERATES, loses power and my rpm goes downhill... I tried to adjust fuel mixture screw and it still bogs. I tried to choke it while running at 5k rpm or higher and it made no difference.
I know all 4 carbs are getting fuel by opening the fuel drain screw and gas pours out on all 4. This problem existed BEFORE I cleaned the carbs. Before I cleaned the carbs, it would not run on idle and was really hard to start so I pour in a total of 2 bottles of fuel injector cleaner for 2 consecutive gas refills. After that, the bogging problem arised. Now the problem still exist after I clean the carbs and ran two tanks of clean 92 octane fuel.
I have NOT clean the pilot needle since I don't think that would cause the bogging. Now I'm thinking too concentrate solution of fuel injectors cleaner has damaged my carbs...or something else is causing the bogging? I have not sync the carbs. I would think sync the carbs would not solve the problem. I have not replace the spark plugs wire either. maybe the wires are arching and cause the bogging?
any suggestions would be greatly appreciated.
thanks, bruce
Answer Bruce, sounds like multiple problems, pehaps. First, using a full bottle of FI cleaner in a 4-5 gallon tank is WAY too much concentration for most any fuel system.
Considerations: You mentioned changing the jets... did you know and properly place the front and rear jets in their right places. Jetting is different from front to rear cylinders.
Carb cleaners can cause rubber parts to swell and this could be affecting anything inside the petcock, fuel pump and fuel lines. Did you remove the float valves in each carburetor and check for any debris that may have backed up inside the passages?
Did you change the fuel filter? It may be restricting the fuel flow, especially if the fuel tank had debris and varnish that was dissolved by the vigorous cleaning of the FI cleaner that was flushed downstream.
The air/fuel adjustments on the carbs are only for idle mixture so will have no effect on engine performance above 1/4 throttle.
To get these carbs on and off, you have to disconnect a lot of vacuum hoses and I am pretty sure that the carbs linkages get tweaked enough to require synchronization again, but you will notice this to be a problem at idle and mid-range when they are off noticeably. Do be sure that all vacuum hoses are connected correctly and that nothing that they are attached to has a problem. There is a purge valve and air cut diaphragms that can cause air leaks and lean running if they are defective, depending on the level of emissions controls on your machine. Calif models are more restricted and have more things to go wrong than the 49 state versions.
I would check the spark plug caps for resistance matches and secure all the plug wires in the coil towers. You might want to run it with the seat and side covers off at night so you can look for any arcing from ignition related components. Check all fuses, fuse holders and electrical connectors for corrosion or loose connections. I think that the plug wires are solid core, but can get corroded on the connection ends. Coil failures or breakdowns are not unheard of on the V4s. Try a fresh set of plugs, too.
If you need to try to clean carbs on the bike, in the future, check the Yamaha Dealers for their slick carb cleaner products. They don't hurt the fuel system components like the commercial car cleaners that are designed for 15-20+ gallon applications per bottle. Sometimes too much of a good thing is not a good thing...
