Topic: First build, working to get 78' CB550K running

[BD-DV07]

Hey all! This is my first post. Glad to be on the forum.

I started trying to get it to start, still trying to troubleshoot as much as possible. I have a great shop nearby but he won't look at it until Oct (out of peak season), but is nice to help me troubleshoot about once every other week over the phone. Right now the guess is the compression is too low so might need a top end rebuild. Waiting on new intake boots since they are all cracked and busted to retest again. At any rate. Here is a picture of the bike right now.

I've done a few small things, put in a DYNA Ignition and coils system, clubman bars, removed front fender, bobbed the rear fender, put a LED tail light on it, plasti-dipped the side covers, and added bar-end mirrors. I also ripped off the old seat vinyl, shaved down the foam with a bread knife, and made a new seat cover with brown marine upholstery. The little bummy things are a bit smaller than I thought since the foam under the vinyl wasn't that think, but It looks ok. I'm stripping the tank and repainting it black, soon. I'll be putting some mini gauges on it once it's up and running because I hate the stock gauge cluster.

[harisuluv]

Welcome to the forum.

What is the basis for diagnosing no start as lack of compression?  Possible but to not even run cause it was too low?  Haven't experienced that myself.  More than likely fuel or electrical.

[BD-DV07]

Hi Harisuluv, Thanks for saying hi!

So without knowing any and all air leakage, the compression test came back (#1-#4) 90psi, 95psi, 95psi, 30psi. The last cylinder I think reads so low because of a air leak in the chain, but will test again once new boots get in. I'm really hoping adjusting the valves and the new boots fixes the compression issue. But right now, it's too low to even sort of start. My mechanic says I should be getting 130-160psi.

It's getting spark, and fuel as far as I can tell. cleaned the carbs a good bit.

[harisuluv]

Yeah that 4th cylinder is not normal if a true reading.  Boots don't actually contain compression, they are just an intake.  You can compression test without the whole carb assy on.  When you do compression test, you do need to have the throttle wide open. 

I'm guessing it's fuel though.  Spark is easy to identify as existing.  Fuel not so much, and people that are newer tend to make too many assumptions.  You can even spray starter fluid (sparingly) or some combustible in the cylinder and see if it coughs.  Simple test, problem pinpointed.

I have seen people that are unfamiliar with these carbs on these boards clean the same rack of carbs a dozen times.  They too, more often than not, think they are NOT the problem.

[BD-DV07]

This is my first old bike so I wouldn't doubt it. Everything I owned before this was early to mid 2000 Honda cruisers, I didn't do much work on them personally.

I'm not super familiar with doing the starter fluid method. Do I do it with the air filter on or off?

I do think a proper rebuild of the carbs will happen before I a top end rebuild. The PO ran ethanol gas it in but I don't think stored it properly. I may try to tune it again, however I don't have a float valve measuring tool.

That being said while on the carb topic. I do notice fuel leaking out from some place of the carb bowls when trying to start. I'm not sure how much fuel sits in the bowls, but I don't feel like it would be a whole lot even when running. I'm not sure if I'm flooding it, or the fuel isn't getting pushed to the engine.

[harisuluv]

You are just trying to introduce fuel (for sure) directly into the cylinder and see if it combusts/does something. 

You can do that by introducing it via the carb side (i.e. airbox removed, throttle open and spray directly into air intake).  Or you could remove the plugs, and spray a little squirt directly into the cylinders.  All the airbox filters etc, all that stuff is unnecessary for this test.

It's not going to run for any significant period of time, but you will pretty much be able to pinpoint your problem in minutes, and will make leaps and bounds in your trouble shooting.