sj413 running realy bad

[new2zukes]

hi all i have a sj413 with a 1300 standard g13a or b cant remember (carb model) i have finally got the warrant for it and now the rego but its runs like a bag of s**t went to work thismorning and just about got cleaned up by a milk tanker as i put my foot down to come onto the main highway motor cut out and im sitting in the middle of the road thinking 'mmm whats next' finally got it going and put the choke in and slowly went backwards to where i started from, had to check my undies then off i went.
the engine was backfireing all the way there only when the foot was past 1/3 throttle. timing is perfect as per suzuki specs, still runs crap at idle, i cant feel any vacuum leaks. have played with float going from one extreme to the other to see if any change and none. am a bit sick of it at the mo but i need it fixed by the end of the week as my safari needs the fuel pump ripping out and sending to auckland so thats about a 4 day turnaround.
if someone has any suggestions as to what could be causing this that would be great. oh and it has had a new seal set put threw the carb and it ran mint before it sat in the shed for 6 months for rust repairs. it has been cleaned about 2 weeks ago. thanks.

martin
p.s sorry for the long winded explanation.
oh and forgot to say that when i put my lights on the revs go up about 1500rpm not sure whats the story there.

[zukmeista]

What is the fuel filter like? And also has the fuel pump been replaced? It is common for the pumps to deteriorate with age sending shit through the carb, the best thing to do is put another filter between pump and carby. The revving up when the lights go on is the idle up solenoid, open up the bonnet and look at the front of the carby with the engine running and get someone to turn the lights on, should be easy to see what moves and needs adjusting, there is a screw to adjust how much the revs increase.

[3.5Pajero]

I was having similar problems with mine dying at the most inappropriate times - people give you funny looks when you rev the sh*t out of it just to get through an intersection in a timely manner.

Check the vacuum advance on the distributor - pull the hose of the carby and suck on it, if it's leaking that could be the cause of the giant flat spot.
How’s the butterfly shaft in the carby body? Excessive wear and could cause your symptoms?

I've also had problems with the vent in the rocker cover blocking up with mayonnaise due to a leaking head gasket - resulted in overpressure in the crankcase and an engine that ran like crap. Blocked off the breather to the inlet manifold and just left the one to the air filter. Probably doesn't suck fumes from the crankcase at idle any more, but the engine runs a whole lot better and there is no overrun when turning the thing off anymore.

Let us know how you get on anyways...

[UBZ]

Manual choke or Auto Choke?
if the revs go up 1500rpm when you turn on the head lights , I would say there is a big air leak in the idle up circuit to start with.

back firing , would imply a timing issue. they can jump a tooth or 2 on the cam belt under hi revs , the crank shaft and cam shaft keyways wear and can shear.
Distributer bearing failure can allow the dissy shaft to move upwards affecting timing . dissy cap can move out of alignment on dissy . mechanical advance in dissy can get stuck .

id also be checking the normal stuff ie fuel filter / pump. crap in the carb jets , vaccum/air leaks on the carb, plugs and leads etc etc .

[tintin]

Manual choke or Auto Choke?
if the revs go up 1500rpm when you turn on the head lights , I would say there is a big air leak in the idle up circuit to start with.

back firing , would imply a timing issue. they can jump a tooth or 2 on the cam belt under hi revs , the crank shaft and cam shaft keyways wear and can shear.
Distributer bearing failure can allow the dissy shaft to move upwards affecting timing . dissy cap can move out of alignment on dissy . mechanical advance in dissy can get stuck .

id also be checking the normal stuff ie fuel filter / pump. crap in the carb jets , vaccum/air leaks on the carb, plugs and leads etc etc .

X2 on the jets, sounds like the same problem I had on my ute. I had a garage check everything electrical and for airleaks, nothing found then they blew the jets out "fixed"

[new2zukes]

hi all thanks for your replys, answers to questions are
fuel filter was put in front of the carb (50mm from inlet into carb) as well as at the fuel pump, there is plenty of fuel getting to the carb.
jets have all been soaked in fuel then blew out with compressed air. new gaskets plunger etc all that comes with a rebuild kit. idle problem when lights go on is sorted thanks.
vac advance working fine no leaks, cant find any vac/air leaks in the carb area. i have a spare carb in the shed which also ran like crap but the butterfly on that one was nackered (leaked threw the shaft ends) the one that is on car at the mo is ok, has little play but no leaks from it. rocker cover vent working fine i disconnected and blocked off inlet manifold hose and vented the other to the engine bay.
timing is set and seems to be constant but every now and then will jump a few degrees (maybe every 6 seconds or so.)
i have used a can of ether as my fuel to see how it runs and seems to run much better so if i were to take a guess it would be in the carb. but that still doesnt explain the back firing. it is only backfiring when you rev it .
have spent a few hours in the shed tonight to check everything but thought it was time to stop annoying my tenants.

[new2zukes]

hi all found out the main problem was the carb was not working properly in one way or another but as its been running so bad for so long it has created black soot in between the valves (id say from all the backfires ) so have pulled the head off and tickled the valves a little. should hopefully get it running Wednesday night.

[new2zukes]

All fixed now valve tickle made the world of difference and a different second hand carb cleaned out and now runs really well. have driven it to town a few times and goes good, even managed to get to 100kph
thanks all for your help.