Topic: 78 750k no power

[invisiblecouch]

I have a nice 1978 750k that I recently got running. Cleaned out the carbs, new plugs, oil, air filter etc. It runs pretty good. But is lacking in power. I've worked on bikes most my life.

It has 19,000 miles and two into two exhaust.
My buddy on his 75 750f that burns oil and hes a bigger guy, walks away from like nothing.

It also has a slight burble/miss in the mid range under load.

I had a 77 550k a couple of years ago that I think would easily take this thing in a drag race.

Are these lean from the factory? Or are the carbs problematic? It seems lean to me. My 550 was way lean with the factory jetting, I had to go up in the mains and drill the pilots a couple thou. That did wonders for that bike.

[Inigo Montoya]

If everything is stock, it will not be too lean. I have a 77 but have teh 78 carbs. I have a k&n in it and never rejetted and it goes like crazy.
So did you clean the carbs or just think you did? I ask as a lot of people do not pull out the idle jets and clean them. You MUST pull them out to do it right.
Also, have you adjusted the valves and checked timing? Either can kill power and tight valves can cause damage.
Have you run the bike and checked the plugs? I know some might disagree but I feel for the 77/78, the plugs should only have a light dusting of tan on the insulator. Anymore and it is probably too rich. If VERY white, then the idle mix is either plugged up or needs to be adjusted. the fuel screws allow a very good range of adjustment.
Also, make sure the accel pump is shooting fuel into each of the 4 carbs.

[XN]

I had about the same problem I followed this http://blog.360.yahoo.com/blog-Sg4KjsE8erQjVxgd6tTWVeKm_ww-?cq=1&l=1&u=5&mx=31&lmt=5 to tear them down. It works very well now 

[cookindaddy]

XN: I have the same bike/carb and I'm interested in your link but it takes me to my own Yahoo profile, which isn't where your carb details are. Is there another link you could give? Thanks

[Inigo Montoya]

It isn't hard. You just need to remember to clean every hole and tube and nook in the carbs. Pull out the jets and clean each hole with a strand of copper wire. The mains unscrew. The idle jets pull out. You just wrap a bit of cloth around the jet and grasp with pliers. Twist while pulling and they will pop out. Avoid wiggling back and worth as that could crack the seat. You can get a carb cleaning tool from honda. It consists of a number of different sized wire that can be used to clean the holes out.
Spray every fuel passage. Clean out the accel pump housing.
It might sound like a lot and a basic cleaning will take at least an hour. If your carbs are dirty, spend 2 hours at least and pay good attention to each carb. You do not need to take them completely apart from each other, just disconnect all tubes and take out the aluminum tubes to allow all the crud to flow out.
Spray and prod EVERY hole. Wear eye protection when doing this.

[BobbyR]

I have a 78K and they were leaned out to appease the EPA. If you modify the exhaust and put on pods it will get worse. I run 120 mains which make it a bit rich. The point Inigo is coreect, you need that level of detail in cleaning the carbs. I had to do mine 3 times to get it right, I could have done it once had I had that advice.

I am not sure what your gearing is which will have an effect on performance. Some geared for lower highway Rpms which will kill the low end. These motors have nothing at low RPMs. 

[Inigo Montoya]

Most 4s don't, that where all those sweet RPMs come into play!

[invisiblecouch]

I did pull the jets and clean them individually. Everything seems fine in the carbs.
It just doesn't pull. Its making noise, that about it. It revs up ok, but its a dog. I always heard these 750's were snappy. Its just a big heavy turd.

I'll probably wait till spring to figure it out. Its getting cold now anyway.

[redschwa]

Don't wait till spring hop on it while it's fresh in your mind!

[XN]

XN: I have the same bike/carb and I'm interested in your link but it takes me to my own Yahoo profile, which isn't where your carb details are. Is there another link you could give? Thanks

That sucks cause it was a good one for someone who has never torn them down before. I get the same thing now...  Pull all the jets as said above clean real good and put em back together (I run 110's for the main). Also make sure your accelerator pump is working squirting in all 4 carbs, bench sync and set the screws per the book. Its ran so good I have not bothered to do a real sync (mostly cause I've had one busy summer) I also set the valve lash, timing, adjusted the cam chain tension.... It really runs awesome for an old dog