I'm at my whits end

I'm working on my 1982 seca 750 and don't understand why when I start my bike up it smells like fuel. I replaced the fuel valve that I got from chacal yesterday and thought that the diaphram was leaking into #3 cylinder and changed the spark plugs as #3 and #4 were real dark fouling out looking. I think my needles are leaking by as when I checked my fuel filter this morning it had no fuel in it. When I started it it blew out fuel smoke. Any suggestions befor I remove the carbs as that is not always fun to do. Is there a way to repair without removing the rack from the motor? Any help would be appreciated. Thanks


PS chacal is the man for your parts as I recieved mine in two days. Thanks Len everything fit great.

 

Hey, I had a smog inspectors licensee for 6 years. a missfire can do the same thing. since I'm sort of sure you don't have a scope, and the carbs are individual, look into a plugged exhaust as a possibility
YOU can't smell Co but H.C. smells like gas. It can be caused by too rich or too lean to fire. the coils are different so its not there either. Call ghost buster or find some who really knows how to use a scope and an infrared. Did you ever notice their are ports in the stock exhaust for infrared samples?

 

padre,
thanks for your insight, but I have pulled the #1 and #2 plugs and they look like they are running fine. When I start it up I don't need any choke, but it does back fire through the exhaust until it gets warmed up then it seems fine. It seems to backfire from both pipes so I'm not sure where the exhaust would be cloged at? Once it gets warmed up it runs great and pulls up thru the entire rev range till about 8,000 rpm and starts to skip arround bucking and surging. I have gone through the carbs and they are clean but I'm still checking on my float needles and will know in the morning if they are sealing. I've heard that the ethenol fuel can get thing sticky so I put some sta-bil in the fuel and we will see what happens maybe they are just a liitle sticky. Thanks for the reply.

 

There are no shortcuts through carburetor land.

You're going to need to pull the rack, and go through the carbs right.

OR, you can keep messing with it forever and you will never get it fixed.

Simple choice: All in or fail. That's the sad reality of it, you can try to talk yourself out of it but science is science and you have to clean and adjust the carbs correctly or continue to have problems.

NO EASY FIX.

 

Sound like the float valves are leaking the fuel into the cylinders.

Backfiring until all the extra fuel is burned out of the exhaust or you may have valve clearance issues...

Gotta pull them carbs, clean, possibly replace float valves, check/reset float levels on them.

 

Thank you all for the info. I'm going to tear into the carbs next week and relpace the needles. Should I replace the seats too? I checked the level today on the fuel filter and it was about half way empty,so that sealed the deal about pulling the rack. It was hard to start this morning, had to charge the battery that I just replaced last week. Could this be from fuel getting into the cylinders?

 

Before you pull the rack, how about pre-diagnose all problems while the bike is assembled and running??

1. Check all 4 float levels with bike on mainstand- - running, and not.
2. Check the function of each individual enrichment plunger, loosen each little fork, and lift while engine is running.
3. Spray water on all 4 header pipes while idling and,
4. adjust the pilot screw all the way in, and out, litening for the CYL to cut off both ways.
5. Check the function of the "slider" piston, assembled, and with the hat removed. (clunk test)

Doing all these tests will give you insight when the carbs are apart.
#1 will tell you if you need to buy needles/seats. And if you need to change a float setting.
#4 will tell you if a Pilot circuit is plugged. All 4 carbs should behave the same.
#5 could be your high speed surge problem.

 

Thanks Wizard, but the rack is off the bike. I tried to start it up after your sugestion but it was totaly blowing fuel smoke.I did get the water bottle on the headers and it seemed that cylender #2 was running cooler than the rest of them.Now that I have the carbs off what should I be looking for? I will be taking them apart tomorrow and getting some carb cleaner for them. Should I use something differnt than carb cleaner? Is there a way to tell if the needles were sticking or should I look for something different? I do have the manual from Haynes and the Genuine Yamaha Service Manual.Thanks in advance for everyones help.

 

OH! I didn't know you were running ethanol, that stuff may have trace amounts of water in it. Sometimes when water and gas mix, they can form a gum that can cause all kinds of carb & fuel line problems. I think the back firing is pretty normal, but I don't have any mufflers. the plugs fire twice per cycle because it has only two coils. I now agree go through the carbs, carefully. Good luck!

I had a 160 C.B. / V.W. spark arrestors and no baffles either, it was a fast little sucker (85 mph +) :wink:

 

Being down-there ... in Florida, ... you have a situation where the Carbs probably NEED to have their Bores refinished.

See if those babies can all pass a "Clunk Test"

If not, ... get some Medium (Gray) ScotchBrite and scrub those Diaphragm Piston Bores until they shine.

 

Some links general useful info' http://www.xjbikes.com/Forums/viewtopic/t=8588.html
Carbs http://xjbikes.com/Forums/viewtopic/p=154226.html
Float levels dry http://www.xjbikes.com/Forums/viewtopic/t=9998/

 

That float level link goes nowhere, Mr Bush.

 

Thanks Mr Wizard, it does now.

 

Ok, carbs are all clean after a week of soaking in cleaner, now I have them back together. Now the question is setting the floats on a 1982 seca 750 dry. I have read the other links that everyone sent and thanks to all but I'm still a little confused. I understand about the mrasurement of 17.5mm for the height of the float and turning the rack on the 45deg angle, but were should I take the measure on the float? Should I measure the top of the float (what would be the bottom of the float as the carbs are upside down) or should I measure to the middle of the float? Hopefully I can get her running monday after noon. Thanks in advance for everyones help.......

 

I am going to get some flak, here, but I would breeze right on by the whole dry settting bit & go straight to the clear tube & fuel method.
I have never got them right dry, right measurement, but when you test wet, miles out. My 2c.

 

Thanks wiz... Hey just woundering do you have a real job, because it seems you are the first person to respond to everyone LOL... Thanks again my friend...

 

I don't have a job, real or imaginary, but it's just coincidental,the timing of my reponse, I just find myself at the PC between coats of paint, or when they are having tea at the test match.

 

Just an update. Got her all back together, set floats wet and gave it a go. She was a liitle stubborn at first but after she warmed up it got better. She was idleing way high but I dident have the air box connected. Finally got those boots from the air box to carbs on (what little buggers those are) and started her up and set the idle. Set the pilot screws to 2.5 turnes out, colortuned and she is running great. I wanted thank everyone for the help you all gave me and tell everyone that is affraid to jump in and tear things appart. Don't sweat it this form can pull you thrugh anything. Thanks again to everyone.

 

You're not done.
Have some fun with that Bike of yours.
Tweak it until it is Fine Tuned.

After a day or two L@@K at the Spark Plugs.
If they are "Brown Bag Beige" ... leave them alone.
If you have a dark one or a light one ... Tweak the Pilot Mixture Screw the with of a Dime each time and ride some more.

After a few weeks of Tweaking, ... you'll have all four on-the-money. Idling like a sewing machine and flying like a Jet Fighter.

 

Ok, had some fun with her, but it seems that the bike takes forever to warm up now. It starts right up but you have to keep stabbing to throttle it will stay running but if you let go of it it just dies. After it gets to full running temp, witch takes over 10 min she runs like a bat out of h*ll. Now I'm talking it takes a good 10 min for warm up even two times arround the block. I've used the choke during start up but it will idel high for a few min then it will come off the high idle and its back to stabing the throttle. I've checked the floats while running and they are in the range. I've checked the boots and they seem fine. What else can I check or adjust to get this thing starting easer. After its fully warm their is no issues with idle and accepts throttle with no hassitation. One more question, what should the draw on the battery be at start up? My tester says arround 10.09 when cold and about 8.90 when at full operating temp. Should I clean out the starter or is it getting heat soaked? Anny advise would help. Sorry for being long winded.

 

I hope this will be the last post on this subject. Update on my progress. I ended up pulling the carbs back off after a few days. It started to run rich again. During the original carb cleaning I reused the original pilot jets not thinking to look at the replacement one I got from Len.So I reset the floats as they seem too low and changed the pilot jets with the new ones from Len. Set the pilots screws at 3 turnes out and WOW she really flies now. Colortuned her and had blue fire in the hole!!!!! I'm going to ride her for a few weeks and keep an eye on the plugs. Thanks to everyone for your help.......