Topic: Just can't get '78 CB550 to start

[Goldbug]

The bike ran with pod filters and no muffler (as purchased) but the carbs leaked. Took the carbs off and had them rebuilt by a member on here, put them back on with the stock air plenum/velocity stacks and a K&N filter and it would not start. If I took the filter off and choked it up, and almost completely blocked the opening to the plenum with my hand it would start and run until I removed my hand.

OK, too much airflow, not enough fuel. So I had a muffler welded on thinking that might help a little and now it won't even start with my hand blocking the plenum opening. Through this process I removed the plugs the bike came with and they looked good. I put in new plugs just in case.

I know I made a lot of changes but I honestly thought, based on what I read here over the years, that putting the stock air plenum back in with new velocity stacks, and putting a muffler on, would help matters.

Carbs are all stock jetting.

Help! I'm trying to sell this bike because I no longer have the space.

[jaguar]

Have a manual?
Walks you though a tune up.
Make sure all of your baseline setting for floats, needles, points ect ect are set.

I would assume you need to invest in a few sets of brass to tune the carbs though

[iron_worker]

Spark on all four?

IW

[Goldbug]

Yes, I had it running two weeks ago. Only thing that has changed is now I have a muffler. That should not affect fuel or spark.

I would say that the evidence would lead us to a fuel issue. But why? The carbs were set up pretty well on a bench by a member here who has done dozens of racks of carbs.

[Goldbug]

I'm going to run a jerry can with some Sea Foam and beat the carbs with a rubber mallet and see if I get any results. That, I think, is the next easiest step before ripping crap apart (which I am trying to avoid, I always have crappy luck with carbs).

[harisuluv]

post some pictures of your setup, it will help a lot.

[jaguar]

The hammer will help more then doing things proper....

[Moffman]

"Rebuilt" carbs can mean a lot of things. It sounds based on what you've told us to be a fuel issue. If the carbs are stock jetting, putting a muffler on and stock airbox would I think make it run better but I wouldn't think it would cause a no start either way.

Start with a process of elimination. Crack the bowl screws, see if fuel is in the bowls. See if it will start on a little carb cleaner.

[Goldbug]

The hammer will help more then doing things proper....

You have never tapped a bowl to unstick a float? Ok...

"Rebuilt" carbs can mean a lot of things.

My carbs were rebuilt by harisuluv. Two years ago now I think. I haven't got this bike to run since then. Just gave up each Spring, drained the bowls, pulled the battery and put it on a tender.

It ran as pictured in my signature thread for the CB550 with the pods and open exhaust. But the carbs eventually leaked fuel so I pulled them and then sent them to harisuluv. Since conventional wisdom says pods are bad I switched the stock air plenum. The bike did not want to start this way but I had tossed the pods already so I couldn't go back.

The bowls have fuel in them. There is something wrong between the float bowls and the cylinder. Maybe from sitting so long they got some varnish, but like I said, I drained the bowls after each attempt.

[harisuluv]

Yes, I had it running two weeks ago. Only thing that has changed is now I have a muffler. That should not affect fuel or spark.

Just to clarify, is this a different bike being discussed?  Just trying to understand what we're talking about.

[Moffman]

If you have fuel in the bowls then there is no need to hit them with a hammer as the floats are working. If the carbs have been sitting for a while I would definitely pull them off and remove the jets and clean them. I've tried stabilizer, draining, all kinds of different stuff but I have to clean my carbs after every season I store it.

[Goldbug]

Yes, I had it running two weeks ago. Only thing that has changed is now I have a muffler. That should not affect fuel or spark.

Just to clarify, is this a different bike being discussed?  Just trying to understand what we're talking about.

We are talking about the same bike through the whole thread. I'm sorry that this is not clear. I got it to run with my hand mostly covering the oval opening on the stock air plenum. If I took my hand away it would die. When I say I can't get it to run I mean that it's does not run normally and is not ride-able. But yes, the engine did technically run for about twenty seconds under the specific conditions I mentioned. And that's about the most I've gotten out of it in two years. I haven't even been able to duplicate that since I put the muffler on.

[harisuluv]

From one of our email exchanges you mentioned:  "It used to have pod filters from the previous owner but I went back to stock airbox but with an old K&N adapter and cone filter."

I'm having trouble visualizing what this setup is.  It would REALLY help if you would post some pictures.  A lot.

You got a number of people in here trying to help you out here, but it's gonna be hard unless we have real data to go on, pics of your plugs, air screw setting, pics of your modified stock setup (?), did you do a vacuum sync yet? 

[Goldbug]

I can try to get pictures. The K&N setup I am talking about is pictured in my CB500 thread in my signature. I took it off that bike and put it on the CB550. As far as I know, the adaptor plate was made in the 1970s and is out of production. Nobody really knows what I'm talking about when I mention it. Basically it attaches a K&N round filter to the stock plenum with an adaptor plate. I do not have a stock airbox, unfortunately.

I did not do a vacuum sync because I never got the bike running long enough to do one.

[harisuluv]

plugs?  fouled, dry, wet, lean, rich?

[Goldbug]

The old plugs were brown, dry and pretty good looking overall. I haven't pulled the new plugs that I put in two weeks ago. I put the new plugs in before attempting to start the bike this year but have not had a chance to pull them.

I'm sorry but I can't give you guys fast answers because the bike is at a friend's house. Before I go back over I am going to recharge the battery. Then I can pull plugs, get pictures, try Ether, etc. I just wanted some ideas because I am sick of going over there and killing the battery without making much progress.

The idle air screws were tried at 1 turn, 1.5 turns, 2 turns and 2.5 turns. I believe on these carbs the more the screws are out the more fuel there is, opposite of pre-77 CB carbs. That's what I read on here.

So what I'm gathering from some of you is that I am not getting fuel into the cylinders because the carbs need cleaned again. Except that I had the same trouble when they were fresh off the bench. My CB500 has inline fuel filters on dual lines going into the carbs. The CB500 just has a line going directly from the petcock to the carb. Is it possible that trash in my tank got into the carbs and blocked the slow speed jet?

[vames]

Is there a chance that the jets are marked as stock but drilled out by the PO to get it to run with pods?

[Goldbug]

Is there a chance that the jets are marked as stock but drilled out by the PO to get it to run with pods?

PO never touched the carbs beyond some cleaning and maybe redo the bowl gaskets. I was surprised it ran with the pods and open exhaust with stock jets. It did not run awesome. But you could run through the gears just fine and ride it around. I only put a few miles on it that way to test it out as I worried about running lean.

[jaguar]

Sounds like you need to pay a local mechanic to fix the bike.

[Goldbug]

That's a silly response. What trouble shooting steps will a mechanic take that I cannot take? If the presentation of information isn't to your satisfaction then don't feel obligated to respond. Thanks.

[jaguar]

That's a silly response. What trouble shooting steps will a mechanic take that I cannot take? If the presentation of information isn't to your satisfaction then don't feel obligated to respond. Thanks.

This isn't something that can be feed via the web.
There is a feel to this.  No insult to say that a person seems to not have it.
If the idea is to solve the problem then you should pay someone local that has an ear for this.  If the idea is to learn then you need a manual (literally walks you through stuff) and a person local with an ear to fix the bike.

See the point is that little can be done on the web.  It's not a real place. 

You are talking about carbs that were cleaned years ago and kinda run and kinda stored.  That doesn't mean much.  It's like saying "ran when parked" or "shinny when new"
You are placing to much stock in things you think are right, and not enough time with a manual and a wrench checking what's rigth.

[Stev-o]

Nobody really knows what I'm talking about when I mention it.

No, we don't, that is why you've been asked for pics.  We want to help but you're not giving the info we need.

[Tews19]

Would you be able to post a short video of it running? I know you mentioned it kinda ran so maybe a video would help.

[eigenvector]

There is one other piece of information that I haven't heard.  When you start it - does it cough, does it act like it's trying to start, or is it flat engine turn-over with no indication of firing?

Everything that I've read on this thread says that this is still probably something fairly simple.  Also something located in those carbs.  The fact that you can start it by blocking up the air inlet says that it's a fuel issue - you indicate as much as well.  So start with the source of the fuel - then work your way down.  Don't jump steps, don't assume, do the checks - you'd be surprised just how twitchy the system can be (don't ask me how I know).

[Goldbug]

It kind of coughs.

One thing I should mention is it only starts to cough if the throttle stop is all the way out. With any throttle whatsoever it just spins flat. So this all leads to no fuel.

I'm just trying to exhaust all possibilities for a fix before pulling the carbs off again or opening them up. I do not really want to do that.