Jump to content
Sign in to follow this  
jonan

83 Honda Shadow - cant get it running :(

Recommended Posts

1983 Honda Shadow VT750C - v-twin

bought it last season not complete.

bought parts and put together, except main fuel tank. new fuel pump, misc cables, brakets, etc

got running. even rode it down the street icon_smile.gif

rinsed the main tank out several times with fresh gas to remove any residue, until gas came out clear.

installed main tank and now it doesnt run.

has spark, backfires through intake and exhaust.

carbs get gummed up. since then ive cleaned the tank and carbs about 4 times. with the same results.

compression is similar in both cylinders. dont remember what it was but it was about 10-15psi lower than specs. i assumed it was this low since it hadent been run for several years.

when it does run for a few mins with throttle at the sweet spot, front cylinder gets hot like operating temp and the rear is cold like its not running. rear plugs are also wet...

suggestions? spring is almost here!!

thanks

Edited by jonan

Share this post


Link to post
Share on other sites

I assume of those parts, you replaced the spark plugs. With a bike that old, I would replace the spark wires also. If they're original, they've got to be shot.

My only other thought, is that problems started with the addition of the gas tank. It must still have gunk in it.

Share this post


Link to post
Share on other sites
This part waved a flag for me. Both cylinders should be warm. I am not familiar with this model... does it have two carbs? I would pull the fuel lines and blow them out with compressed air' date=' for starters. Since it ran fine before you 'cleaned' the tank I would guess something loosened and became lodged in the line somewhere. Not saying this is the problem but it's where I would start, especially if the rear cylinder isn't warm after running.[/quote']

ya carb for each cyl.

there is also a fuel filter after the reserve tank and before the pump. has a main fuel line from the pump and has a T that feeds each carb the line to each is like 2in.

ive flushed the fuel sys several times now.

yes spark plugs were replaced. thats the first thing i do when ever i buy something with an engine :)

sorry i left that out. the rear cyl plugs are wet... plenty of spark though...

Share this post


Link to post
Share on other sites

Check to see if there is a vacuum line not connected or if a fuel line may have gotten pinched when you put the tank on.

Share this post


Link to post
Share on other sites

Im saying the carbs need adjusted. If the rear cylinder plug is wet, its most likely flooding.

Share this post


Link to post
Share on other sites

Drain the water out of the crankcase. It worked for Blake....

Share this post


Link to post
Share on other sites

there are 2 rubber boots in the carb. these get brittle over time and tend to rip or tear. i speak for experience having resurected an old shadow myself. check these boots i would almost bet money they are ripped allowing too much air in the fuel mixture. the boots arent cheap, i think i paid 120 bones a few yrs ago.

Share this post


Link to post
Share on other sites

you can wrap them in saran wrap for a very temporary fix :)

Share this post


Link to post
Share on other sites

just like this only no highway bars, front bag, or rear rack :)

CIMG2349.jpg

Share this post


Link to post
Share on other sites

It ran then you cleaned the tank and the carbs 4 times and now it doesn't run. I suspect the carb float on the rear cylinder is set to high filling the bowl with to much gas and flooding the engine.

Good Luck

Share this post


Link to post
Share on other sites
It ran then you cleaned the tank and the carbs 4 times and now it doesn't run. I suspect the carb float on the rear cylinder is set to high filling the bowl with to much gas and flooding the engine.

Good Luck

i like this one.

i'll be working on it over spring break which is in a week and a half.

more ideas welcome.

thanks guys i'll let everyone know how it goes!

Share this post


Link to post
Share on other sites

well i spent the weekend with my dad and cleaned the carbs yet again...

replaced all the fuel hose, filiter and fittings, with new ones, shoved a small funnel in the end of the fuel hose put some gas in it and fired right up!!! didnt even have to choke it :cool:

we also went through the cooling system and found out the rad fan is fucked, whoever installed it put the weep hole facing up... also the thermostatic switch, that controls the fan, is also done...

after letting it run for 5-10 mins also found out the rectifier/regulator isnt really working, only 12.2v at 2k rpms :(

i still need to take both the main and reserve fuel tank and clean and seal them prolly gonna use POR15, recommended by many here. i left the key in the bike at my dads though :doh:

gonna go through the boxes of parts i have in my garage and hopefully get it all put back together once finals are over. then take it and gets some tags and be cruisin :D

Share this post


Link to post
Share on other sites

nice! so the boots were okay and the float was set correctly on the rear cylinder?

about the rectifier though, it may not be bad. Most charging systems on motorcycles don't work until higher rpm, so it will not charge the system at idle. Consult a manual to confirm, but I don't think your rectifier/regulator is bad.

Raise the RPMs (at least 3500rpm) and see if you get a higher voltage

Share this post


Link to post
Share on other sites
nice! so the boots were okay and the float was set correctly on the rear cylinder?

about the rectifier though, it may not be bad. Most charging systems on motorcycles don't work until higher rpm, so it will not charge the system at idle. Consult a manual to confirm, but I don't think your rectifier/regulator is bad.

Raise the RPMs (at least 3500rpm) and see if you get a higher voltage

boots are good, floats were right on.

we tested the r/r from idle to about 4000rpm still wasnt within the specs listed :sad: 12.2v at 2000rpms was the highest it got...

i'll update when i get further along :grin:

Share this post


Link to post
Share on other sites

well i put about 300 miles on it and it was doing just great. until a pilot screw fell out.... now its not running like it was, i would say its running fair to poor...

front cylinder is running really hot compared to the rear cylinder.

its had two full tanks of high test through it.

radiator fan runns when supposed to.

tested and is with in specs: thermostaic switch and thermostat.

im sure the carbs need tinkered with again to get it running better, the book says i need to use a tach that is capable of reading a change as small as 50rpms to properly "tune" the carbs. does anyone have this tool?

also brand new stator lights are rediculously bright now and the battery is being charged with the correct voltage!

im thinking of flushing the cooling system again, replacing the thermostat, rad cap, all hoses and clamps and possibly the water pump.

Edited by jonan

Share this post


Link to post
Share on other sites

If rear cylinder is running cold, I'd agree with the check coil / wires crowd, CDI, who knows what kind of gremlins lie beneath

Share this post


Link to post
Share on other sites

ive gone through the electrical system now and everything tests with in specs.

i replaced the spark plugs just because and the rear cyl is still running significantly cooler than the front.

its idling really smooth, after adjusting the pilot screws but its still running cooler than the front, and it back fires when i crack the throttle and hangs for a while. ive traced the throttle cables and they are not being pinched or are kinked.

the book says i need a portable tachometer capable of reading a change in 50rpms to adjust them properly, and im gonna have to believe this is the problem, after using my ears to adjust the pilot screw the rear cyl temp has increase but the front cyl is still much hotter and it still back fires and hangs

does anyone have a portable tach i could borrow? or know where i could pick one up? or know of a good brand?

Share this post


Link to post
Share on other sites

Have you syncronized the carbs? Made a HUGE difference on my Interceptor. Visually setting them was definately needed to get things close, but using a carb tuner and setting them precisely made things even better!

For setting the carbs, i use my "calibrated" ear. It's something I've always been able to do on cars, setting timing and adjusting idle mixture on carbs, and I just brought that skill out of retirement (thanks to EFI, I rarely use it!) for use on the bikes! I won't claim that it's the best way, but it works for me!

Share this post


Link to post
Share on other sites
Have you syncronized the carbs? Made a HUGE difference on my Interceptor. Visually setting them was definately needed to get things close, but using a carb tuner and setting them precisely made things even better!

For setting the carbs, i use my "calibrated" ear. It's something I've always been able to do on cars, setting timing and adjusting idle mixture on carbs, and I just brought that skill out of retirement (thanks to EFI, I rarely use it!) for use on the bikes! I won't claim that it's the best way, but it works for me!

i followed the instructions in the book for setting the carbs and got it to idle much smoother, but still running cooler, if at all...

what exactly is syncronizing the carbs? is it adjusting the pilot screws? other than the idle screw there are no other screws to adjust...

the seasons almost over and ive only been able to put 400 miles on it :(

someone help! btw im broke so ive been tinkering and reading but its still not running right...

Let me know if you do find someone with a portable tach... I gotta check mine too!

if anyone knows a brand or what a good one to buy is i will just buy one and let you borrow it.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×