scratching my head - it just doesn't seem to run right

I got this seca last fall, and have been tinkering with it. Here is what I have done so far:

- removed rear wheel to check brakes & lube drive
- changed oil, filter, and dif lube.
- new fuse block
- removed, cleaned, adjusted, and sync carbs
- check timing
- cleaned gas tank & rebuild petcock.
- basic once over for loose/missing nuts bolts.
- check air pressure in tires
- new air filter

Now the problem...

1) It seems to have a vacuum leak somewhere. Just out of the blue, it will rev up and stay there. I checked the cable, and did the propane leak test. I did not see any indication of a leak when sync'n the carbs. (I have mercury sticks)

2) The brake indicator is on (red error light doesn't work), but the fluid is full. According to the book, it comes on when the fluid is low. Question - can it trip the light if there is an air bubble in the line? I did not do anything with the front end.

3) tail lights don't work. The previous owner just took a quick connect and spliced the wire to power for the light. (I will be searching that out today) & the dash lights don't work.


Any ideas of what to look for?

Thanks

 

Check valve clearances, check cylinder compression

 

I did adjust the valves - forgot to put it in post.

Compression 105-110 all cylinders.
Plugs dirty brown - #4 running a bit rich, but not too bad

I am getting 4 volts at the terminal block to the tail light, and I replaced bulbs in dash with ones I know work - they still don't work either.

It looks like that feeds from the computer. Could it be something in the computer that is bad?

*** When I rev the engine, it hesitates on acceleration and doesn't rev down right away. Almost as if the slides were lagging. They snapped right down when I put the in, but slid down slow when I put the caps on. Are the caps suppose to vent?

 

1) did you adjust the idle rod screw when the engine was warmed up?

Get an Ohm meter and happy hunting

 

if it revs up on it's own i don't think it would be sticky slides, if you give it gas and it doesn't come back down however, that might indicate slides. the caps seal the diaphragm, the only vent to the cap is through the little hole in the bottom of the slide, that is why they fall slow when the caps are on, totally normal.

do you have a colortune plug to check your idle mix? or did you pull the plugs to check for color? also when you did the sync did you block the YICS ports? if not, your sync may be off.

 

I found the wiring problem - 5A inline fuse inside the headlight assembly.

I don't have a colortune. I set the idle mixture screw to 2.5 turns out.
And yes I used the sync block. Sink is on almost dead on w/mercury sticks.

I am thinking that the rev is caused by lack of gas. I don't have much in the tank. I plan on running up to the station and filling it to see if that is an issue - I probably only have a half gallon or so max in there now. It doesn't even register on the fuel gauge.

I still can't figure out why the brake indicator is on. The master cylinder is full, and the brakes work. I may bleed them just to be sure there is no air in the lines. They do feel a bit squishy.

It has been about 20 years since I have had a bike like this, so I don't remember everything about it. I had the Maxim - no computer panel.

I'll post pics when I get it done. I need to find a spring to hold the right side cover on. (broken tab by tank - I just drilled a small hole, and will put a spring across under the tank to hold it in place until I can find another one)

 

c21, I doubt that low fuel will cause a high RPM. You either have a hung up cable, a vacuum leak or an incorrectly set idle screw.
The brake light could be a stuck switch in the master cylinder (I have this problem). Black/white and Black wire in the headlight bucket, check them for tightness/security/voltage/continuity. The switch should read open with the reservoir full.
I have pictures of a successful side-panel repair I made using two different methods if you are interested in fixing yours. Let me know and I'll email you them.

 

on your brake light warning did u disconnect the wire splice once u replaced ur fuse in the head light bucket? if not do that and should go away.

 

No sure if the brake light will come on if the bulbs are bad in the tail light. I know on my 1100 there is a indiacator light for the tail light so the rider knows he has lights out.

If its the brake warning light it is mostlikely the float switch in the master cylinder.

MN

 

I have found two types of Air Leaks that are difficult to detect on two Seca Bikes:

An Intake Manifold to Cylinder Head --> Intermittent, ... only happens upon heated-up ~ upper-revving.

Hose Clamp misplacement --> "Incision" on the Intake Manifold which looks like a crack --> forming -- but, becomes a severe leak when the throttles are opened.

 

Another hidden source of air leaks-- hard to test for: throttle shaft seals could be worn out.

Dave Fox

 

Short version: it may be improperly seated diaphragms.

Longer version: I had a similar issue with the revs climbing on their own and the revs not coming down with a throttle blip.

I had just finished cleaning my carbs. The bike started right up and worked fine at first, but gradually the problem got worse. When the bike was not running, the throttle would open and snap closed as expected, but when running seemed to be held open. If I reached in, I could push down on the linkage and bring down the revs, but they would start climbing again if I let up.

After a couple of weeks of on again/off again screwing about, I ruled out cabling and other external factors and pulled the carbs again. I figured it to be some sort of vacuum leak. As I was taking off the diaphragm covers, I noticed that one of the diaphragms did not seem to be completely seated. Did another once over and when I was reassembling, I put a little film of silicone grease on the underside of the edge of the diaphragm and made sure it was completely sealed into the channel before buttoning everything up. Bench-synced and reinstalled the carbs, hit the starter and she fired up instantly with perfect throttle action.

Outside of needing to dial back the idle (she ran to 6000 rpms immediately), she is running beautifully. Must have done a helluva bench-sync, because I still haven't performed a full sync on it. In fact, she has never run this well in the 3 years I've had it, I don't really want to take a chance of screwing it up. Maybe someday soon, but I'm having too much fun riding it.

 

I disconnected the master cylinder sensor and jumped it, along with making a battery sensor eliminator. That took care of all the idiot lights.

I took the bike out on it's maiden voyage... to the gas station, to see how it runs. It just wouldn't rev down. It would idle at about 4k for a minute, then slowly come down to normal idle. When I arrived at the gas station, I checked everything out, and saw the head gasket was leaking at #1 cylinder.

I took it home, stripped the engine down, and ordered all the parts from Len - $400 for gaskets and rings. I got a new needle/seat for $11 (Yamaha shop wanted $107. For just one!) I figured if I have to tear down the engine for a head gasket, I'll just rering it too. I was only getting 100-110 compression on all cylinders.

Now cleaning, honing, and painting the jugs. Then when that is done, I am going to tear into the head. Polish the ports, lap the valves and do a leak test. I should have a brand new engine when I am done.

I will recheck the carb slides, and throttle shaft play too. (I really hope it was just the leaky head gasket causing the problem.)

Thanks for all the suggestions.

Hope to have it on the road by next Monday.