Can't get her started..

jacksondee

jacksondee

Active Member
Hey guys, 1981 CB750F

I just did the RSC Carb mod and the pods are on and the leaky O rings in the carb were replaced. I have no fuel leaks anywhere, the throttle and choke cables are connected properly.

I just can't get her started. She did fire up for about 10 seconds, then died, and I haven't got her back up since. I'm getting loud backfires out of the exhaust and it sounds like it's rumbling, but it just won't start. I've burned through a fully charged battery now.

I have a Kerker 4-1, and the baffle is removed. Do I need more backpressure or something now that the carb has been modded? Put the baffle back in?

The bike hasn't been started in the first place since December, when I brought it inside and took it apart to do the carb mod and add pods.

Do I need to change the oil first? Is the old oil too sticky at the bottom of the bike since it hasn't run in a while? I thought I would get it running first and warm it up, then put in fresh oil.

I pulled all the spark plugs, which are also brand new, and two of them looked like they had a little bit of ash on them, like they are trying to fire..

I've never done this before so I don't even really know what to look for.
 
Start at square 1.

Can chain adjustment
Valve lash
Timing using a test light

Then mess around trying to start it. When did you last do the above?
 
Tim said:
Start at square 1.

Can chain adjustment
Valve lash
Timing using a test light

Then mess around trying to start it. When did you last do the above?
Click to expand...

Heh. I don't know how to do any of those things. I bought it last summer and it started every time I asked it too without issue. Very reliable. I was hoping I could mod the carb and get it to fire up reliably again, but maybe that was wishful thinking..

Last week it wouldn't start and I realized it was leaking fuel from a bad O ring in the carb. I've fixed that leak now but am stuck again. I thought perhaps the leak was the only issue and it would fire right up once fixed. I was wrong!

I've never worked on a bike before, I've learned a lot this winter dismantling, cleaning and then modding the carb, but have not yet read up on the things you've suggested.
 
Get a manual. Those are all dead easy things that take 10 minutes and a 10mm wrench. Nothing fancy or hard and running a bike without having done them is going to frustrate you to no end.

Sent from my Nexus 5 using Tapatalk
 
Nope. Shouldn't be the case. Those are all static adjustments that have to be set up right before the engine even has a chance of running.
 
is this what you mean?

what is 'valve lash' ?

camchain_zps1342b834.jpg
 
I will give you an example of things can just from good to just bad.

Last year I had my bike running a few times. This year after replacing a few things I got the bike running again. Let it sit for 2 days the bike wouldn't start.

Pulled the plugs and tried to get some spark.. Nothing.. Reseated everything and got a bit of orange spark (bad). So I pulled the plug caps off and the are both reading 0.

So just cause it worked once don't mean it will the next day.
 
if it was running when parked then your valves are fine,for now, they wouldn't all of the sudden just jump out of running condition because you parked the bike
something simple is likely wrong whatever you changed has to be causing the issue
and put the goddam baffle back in unless you are only racing
 
VonYinzer said:
Amen to the baffles. Don't be that guy.

Also, what the hell is the RSC carb mod?
Click to expand...

Heh. The guy who sold it to me had the baffle out and I rode it like that allllllll last summer. I guess I was THAT guy.

She fired up! Right after I loosened then re-tightened the cam chain bolts.. Thanks! I'm working on adjusting the pilot screws right now. The tool I bought is kind of a b*tch to use...

She does take quite a crank to get started, and she seems to prefer if I don't use the choke. Pre-mod, she would only start with a full pull on the choke cable...

The RSC mod is from the 1100F.net site. Honda created it to make DOHC carbs run nice with pods... Apparently, if I did it properly, it should run really really nice with pods. 10-15% more power or so too, I guess...
 
jacksondee said:
Heh. The guy who sold it to me had the baffle out and I rode it like that allllllll last summer. I guess I was THAT guy.

She fired up! Right after I loosened then re-tightened the cam chain bolts.. Thanks! I'm working on adjusting the pilot screws right now. The tool I bought is kind of a b*tch to use...

She does take quite a crank to get started, and she seems to prefer if I don't use the choke. Pre-mod, she would only start with a full pull on the choke cable...

The RSC mod is from the 1100F.net site. Honda created it to make DOHC carbs run nice with pods... Apparently, if I did it properly, it should run really really nice with pods. 10-15% more power or so too, I guess...
Click to expand...

You ran without baffles for that long and now you do something that you think will yield 10-15% more power?

I have some muffler bearings for sale.
 
one great powermod is to leave the cam chain adjuster bolts slightly loose ;)
it allows the cam timing to self float into the best powerband
 
firebane said:
You ran without baffles for that long and now you do something that you think will yield 10-15% more power?

I have some muffler bearings for sale.
Click to expand...

I don't exactly know what I'm doing man. I bought the bike last summer and took it apart for the first time ever this winter. I'm learning as I go, I've never done any kind of work on a bike in my life. I was pretty happy I dismantled the entire carb and put it back together.

I don't really care about the extra power, the mod was more so to make the DOHC carb play nice with pods. I knew almost immediately after buying the bike that I liked the visual aesthetic of pods. After a bit of reading, everyone hates DOHC carbs and pods. This mod seemed to be the answer to make it 'easier' to run with pods.

Anyways, are you saying leaving the baffle in is much better for the bike?
 
The crankcase breather is leaking oil like its getting paid to do so..

It stutters a bit when I rev the throttle over 3000 rpm. Time to learn how to do pilot screws and carb tune..
 
Stop.

Just leave the carbs alone for now.

When you're having engine troubles there is a distinct order in which you should be troubleshooting and the carbs are what you do last.

At its simplest, an gasoline engine needs three (and only three) things to run.

1.) A spark introduced at the correct point in time
2.) Enough compression such that the flame front can effectively propagate
3.) The correct ratio of fuel to air for combustion to take place

Items one and two are easy and fast to check, so they should ALWAYS be tested before dicking around with the carbs (which can take days).

If you don't have a timing light (aka strobe light), get one. If you don't want to get one, just take your bike to a mechanic now and you'll save yourself a ton of time and trouble. Same goes for a compression testing kit. You can get both at Harbor Freight for under $80.

First up, test timing by hooking up the light to the spark plug wire and aiming the strobe at the timing marks on the side of the crank. This will require that you take off the side engine cover. See your manual for the proper procedure. Get someone to hold down the starter button while you're aiming the light at the timing marks and make sure the light flashes at the appropriate mark.

http://www.youtube.com/watch?v=-YTb6JGCXH0

Next, check compression. Pull all the spark plugs and hook up the compression tester to the first spark plug hole. Open the throttle all of the way and turn the engine over for a couple of seconds with the starter. You should see around 150 PSI. Repeat for each cylinder. Ideally all cylinders will be within 5% of each other. The closer the better.

Now that you've tested items one and two in our list, you can mess with the carbs to your heart's content knowing the spark and compression and not going to be the problem.
 
Very cool, thanks Sonreir.. Good info. Since it was running fine last season I was hoping to be able to mess with the carb, plug it back in, and fire her right up. I am learning as I go....

The wife is going to be super happy about me needing more specialty tools.. :o

I have plans to buy another bike before this coming winter and try and tune it up as well, so I know I should have this stuff in the toolchest anyways.

Can you tell me if the timing light in the video, the one that also reads RPMs, will that work for the pilot screw adjustment procedure? The manual says I want a "tach with 50rpm graduations," and I've not had any success asking around exactly what kind of tach that is. I also haven't had any luck searching the interwebs because typing in 'tach with 50rpm graduations' yields a bunch of expensive handlebar mounted ones..

Maybe I can kill two birds with one stone getting the timing light with the RPM reader on it?
 
jacksondee said:
Can you tell me if the timing light in the video, the one that also reads RPMs, will that work for the pilot screw adjustment procedure? The manual says I want a "tach with 50rpm graduations," and I've not had any success asking around exactly what kind of tach that is. I also haven't had any luck searching the interwebs because typing in 'tach with 50rpm graduations' yields a bunch of expensive handlebar mounted ones..

Maybe I can kill two birds with one stone getting the timing light with the RPM reader on it?
Click to expand...

Definitely an idea. The cheaper strobes won't read out the RPMs, so you could be looking at spending more for that option, though.

That said, I think most people's ears are good enough to detect a rise or fall in the RPMs, so a precise readout isn't strictly necessary.
 
My compression is f*cked!!!

Cylinder 1
150

Cylinder 2
30

Cylinder 3
120

Cylinder 4
150

I think the book says a big reason for this can be messed up valve clearance?!
I just got a feeler gauge and micrometer so thats the very next thing on the list..

I can't check the timing just yet. The phillips screws are in there waaaay to tight and appear to have been sprayed with some gunk before being screwed in. I need a MUCH bigger screwdriver to get them out..
 
Sounds like you could be fighting multiple issues. Get the compression sorted out first. Hopefully it's just a valve clearance issue. Other things start costing a lot of money, very quickly.
 
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