'82 Seca 750 Refresh Project: Now Scooby's Bike

Yeah, I guess. These WERE new plugs. Couldn't hurt I guess...

Though... Like you said with the likelihood of two coils failing at the same time... I'm having the exact same problem across all four.

 

if all you did was get into the float bowl your sync should be good, check it, give it a tweek.

 

I agree with you. In the moments where the intake is pulling vacuum, looks like all silver indicators in the sync gauge look even... but just during those moments... those fleeting little moments...

I'm going to pull the carbs again... I'm going in without a plan... cover me...

 

You should be seeing vacuum all the time that the engine is running. Even if you're just turining it over with the starter there should be enough vacuum to show on the gauges.

Mind satisfying some curiosity with a video of what you're seeing?

 

When I do a bench synch ,I cut two business cards in half put one each , under the butterfly plate ,turn the synch screw while pulling on card till I get slight resistance on the card , once I get this on all four carbs hold carbs up to a strong light source you should see a slight gap at bottom of the plate. If and this is a big if your plate is not fully seated you might find one plate is slightly off( I know it happened on my carbs , one plate was off ever so slight ) just my bid to help cheers

 

Of course. Glad I didn’t pull carbs yet. Will go through the attempted start up scenario tomorrow and record it.

As for the fleeting moment thing... that was my attempt at drama. What I was getting as was that it isn’t running long before I allow it to stall or decide to shut it down. Just to scared to beak something.

 

do a compression check on one cylinder. when mine is running real slow before a stall the cam chain starts slapping around. could yours have jumped a tooth? is it that bad?

 

I have to look into this.

Went out and attempted it again for the purposes of recording video. It was a bit of a juggle with trying to keep her running, recording and of course keeping the inexpensive (CHEAP) tuning fuel bottle filled (it's only 300ml). It drains fast... another symptom of the larger problem... perhaps.

You'll see around 2 min, I began backing off the choke so you can see and hear what happens. At the audible pop, there is a push of air that comes from the airbox intake. Seems like there is a delay in the response from the carb tune. It also does not display very high at all, unless on throttle.

 

1. Do a compression check. There should be more vacuum than that at idle.

2. At 2 min of runtime from cold the engine is not usually going to be warm enough to start backing the enrichment off.

3. That pop is a backfire (a true backfire through the carbs) which is a sign of being rich (likely from all that messing you did with the throttle during warmup).

4. Can you start it and keep it idling without turning the throttle?

 

Will do... Engine cold? Hot? Or does it matter? Also... All plugs come out, throttle open on start button and completely disconnect the coils (thin wires) from their connectors, correct?

Yes. I just got it going and stayed on for at least 5 min till I shut it down. Choke was in the ON position. Forgot my phone in the house so I had to scramble back in to get it to record the following... Here is 2+ min of that run.

I am not touching throttle at all... It is rising and falling on it's own.

 

Turn the carbtune upside down and use it that way

 

unplug the tci not the coils.... and if possible use a car battery when doing compression test


hows the voltage output of the charging system?

 

I'm not sure I follow you on this one.

I did the compression test.

No car battery, but what I did was I checked each cylinder with a full state of the motorcycle battery. I use the Battery Tender Jr which is great for bringing the battery back up to full.
Each cylinder checked one at a time with approx. 25 min between each for the tender to refresh the battery.

Engine cold. TCI disconnected. All plugs out. Admittedly it is a Harbor Freight compression tool, but the results were:
#1. 120 (120+ but not 125)
#2. 125
#3. 130
#4. 130

I believe Low Spec is 128

I can check if you give me some direction on that.

 

Just watched the video , okay here is observation when I use the Morgan tune the column should be about 1 to 2 inches on all 4 looks like yours are at bottom , I would try turning synch screws in till mercury increases in height till you can get them to equal an even height.

 

if the carbtune is trusted. the only thing that could affect vacuum across all four is the yics port

 

in this link it will tell you out put voltages of your charging system alsi test at higher rpm it should go no higher than 14.8 volts. just want to make sure you have enough out put to keep the TCI firing.
The Ultimate Relay, Switch, Sensor, and Diodes Guide

XJ650 and XJ750 air-cooled engines:
Minimum: 128 psi
Standard: 156 psi
Maximum: 171 psi
Max. variance between lowest and highest: 14 psi < this spec is the important one

a) make sure the engine is warm (at operating temperature).
b) remove all spark plugs, and then stick the plugs back into their caps and make sure the plugs are grounded to the cylinder head (or even better, disconnect your TCI unit).
c) remove the airbox filter lid and the air filter.
e) open the throttle FULLY and keep it open during testing.

 

Hello friends. I want to thank all of you for your comments and suggestions. Work has taken most of my free time over the last month and a half or so. While I have not sorted my problem out yet, I did have some time to devote to the project over the last two days.

I decided to pull the carbs again. When I pulled the set out, I found that slide #2 was stuck in the down position. I mean REALLY STUCK! I couldn't free it up with the tip of my finger. A flat head screwdriver did the trick... so I decided to pull the tops and bottoms off (did not separate the set) as well as slides, needles, jets, mixture screws, etc. give the bores and slides a buffing with a small soft wheel and put everything back together.

Bench sync is done again and wet set looks good.

Question that comes to mind is this...

Would the engine start and idle (all be it terribly) with a slide stuck in the down position? If this is the case, it would make sense that the exhaust for #2 get hot, signaling (to me) a firing plug... but obviously once running, #2 would not be "pulling it's weight" at throttle thereby leaving the other cylinders have to do more than their fair share in a less than harmonious situation. Then of course I'm over enriching things with the choke lever... ultimately making things worse... Black sooty plugs anyone???

I've run out of time to get the carbs back on the bike to see what the results are... Harumph....

Will update again...

 

the bike runs off of the pilot jet until you get to 2k to 3k rpm thats when the main jets start to kick in.
so the bike will start with slide stuck.

 

This feels like good news. I wish I had the time to get out there and reinstall the carbs. I hear them calling me!

 

Inlet rubber leak? on 1 or more carbs?
( or the dreaded carb butterfly rod seal leak(s)?

I'd love to know if you can get it running OFF choke, what it looks like after a high speed run (old fashioned hi speed plug chop)