L18 engine problem

[620connor]

My 74 620 is running like crap and i cant figure out why. When it starts up it sputters 2-3 times and then idles normaly, when i start to drive off it kicks and almost dies at about 1500-2000 rpm's. When i get on the road and give it about 25 percent throttle it slighty kicks me back and forth struggleing to pull through the entire rpm range.. it does this trough all four gears. But when i give it full trottle the engine feels okay and has good power, but when i shift into the next gear there is a pause (like it almost dies) and then it slams me back in my seat and then the power feels good again as im still going full throttle. It does this through all 4 gears. If i turn it off and wait about 10 minutes and try to drive it again while the engine is still warm it will die and not start up. But then it will start the next day when the engine is cold. The truck has a brand new weber carb on it, new spark plugs, wires, cap, rotor, points, coil and resister. Does anyone know what could be wrong? Any help would be very much appreciated. Thanks.

[ggzilla]

one cause of these symptoms is water or crud in the carburetor fuel bowl. Remove the jets, let it drain and put them back in. It's pretty easy to do if you have the Hitachi. I dunno if the Nikki is the same or n ot.

[MicroMachinery]

It does sound like the primary jet getting plugged, but if you have a good fuel filter and brand new Weber, that isn't very likely.. however it is possible.

 

Another thought is that if you have the dual points distributor, it's could be the 2nd(Retarded) set of points doing their job. I disabled mine and set my timing to the advanced set. Those only affect 3rd and 4th(cruise), however.

 

What is the carb jetted for? Do you know? I have a 32/36 weber on my L20b, and I'm fairly certain it's jetted for a smaller engine, as it doesn't pick up and go unless I have both barrels opened up(pedal on the floor)

[620connor]

It does sound like the primary jet getting plugged, but if you have a good fuel filter and brand new Weber, that isn't very likely.. however it is possible.

 

Another thought is that if you have the dual points distributor, it's could be the 2nd(Retarded) set of points doing their job. I disabled mine and set my timing to the advanced set. Those only affect 3rd and 4th(cruise), however.

 

What is the carb jetted for? Do you know? I have a 32/36 weber on my L20b, and I'm fairly certain it's jetted for a smaller engine, as it doesn't pick up and go unless I have both barrels opened up(pedal on the floor)

Im not sure what its jetted for, its jetted the way it comes from the factory. Its a 34 DGEC weber, i sent it back to the weber factory thinking it was the carb and they pulled it apart and said everything was perfect.

[620connor]

Could it be my timing chain? It is really streched out.

[datzenmike]

34 DGEC is too big for an L18 hell the 32/36 is more than needed. The 34/34 is used on motors well over twice the size of the L18. Primary is too big, smaller would be better.

[banzai510(hainz)]

was it working good before the carb swap?

 

olddatsuns.com read it. ck the simple things first.

 

could be loose condensor on ther points. loose dizzy shaft wiggel,valve lash, set timming

[620connor]

34 DGEC is too big for an L18 hell the 32/36 is more than needed. The 34/34 is used on motors well over twice the size of the L18. Primary is too big, smaller would be better.

I have a fuel regulator on it, i realized it was too big. Its set for the "100hp and under setting" so it should be fine.

[620connor]

was it working good before the carb swap?

 

olddatsuns.com read it. ck the simple things first.

 

could be loose condensor on ther points. loose dizzy shaft wiggel,valve lash, set timming

It wasnt working before the swap, i installed the weber and it ran good for a while.. and then it started running worse than ever. Ive checked/done all of that stuff but no luck.

[620connor]

Well i guess my last option is to take it to a professional shop. No one can figure out whats wrong with the damn thing.. its crazy, and i need it running by the time school starts up again. Every single thing i do to this truck does nothing to make it run better. Ive had a few of my dad's mechanic buddys come over and try to work on it but they cant figure out whats wrong with it either. Nothing simple is being overlooked... Does anyone have any other ideas why it could be running like this?

[banzai510(hainz)]

ck the points.

You said you replaced everything n the ignition.

If the points look like they are pitted or burnt up already then maybe you put a wrong value coil in and its arching the points. soemtimes I put the old stuff back in and see if that works.

This is a simple motor. and ignition but if the wrong stuff is installed it will fuck it. You sure the coils and ballast was specific to a datsun.

 

Fuel regulator? whats that for? most early 620 use a manual fuel pump and they are the low pressure type of around 3 pounds or so. If you have a electric pump dial it down to under 4 pounds. otherwise it could screw up the carb

[620connor]

ck the points.

You said you replaced everything n the ignition.

If the points look like they are pitted or burnt up already then maybe you put a wrong value coil in and its arching the points. soemtimes I put the old stuff back in and see if that works.

This is a simple motor. and ignition but if the wrong stuff is installed it will fuck it. You sure the coils and ballast was specific to a datsun.

 

Fuel regulator? whats that for? most early 620 use a manual fuel pump and they are the low pressure type of around 3 pounds or so. If you have a electric pump dial it down to under 4 pounds. otherwise it could screw up the carb

The points are in perfect shape. I have 3 datsun coils that ive tryed and it runs like crap with all of them, the coil im running now is a L20b coil and resistor. I know its a simple motor.. thats why i dont understand why it wont run. The carb on my truck is to big and was over fueling so i installed a manual fuel regulater, you just connect the fuel lines to it. It has number settings on it and only allows so much fuel to enter the carb depending on how i set it. Its set correctly. Would electronic ignition help this problem possibly?

[Rob W.]

Have you checked the float bowl for water? Drained the fuel tank and started with all new gas? Have you burnt a full tank of gas since you've had this problem? If all the hard parts are right maybe it just bad fuel. Try a fuel treatment maybe that removes the water and adds a bit of octane. It could just be bad gas. Especially if it was fine and than suddenly real bad. I have had similar issues with crappy old gas in motorcycles. Drained the fuel added fresh and presto no more problem. It would be worth a try before you shell out big money and let someone put there grubby paws all over your fine machine.

[620connor]

Have you checked the float bowl for water? Drained the fuel tank and started with all new gas? Have you burnt a full tank of gas since you've had this problem? If all the hard parts are right maybe it just bad fuel. Try a fuel treatment maybe that removes the water and adds a bit of octane. It could just be bad gas. Especially if it was fine and than suddenly real bad. I have had similar issues with crappy old gas in motorcycles. Drained the fuel added fresh and presto no more problem. It would be worth a try before you shell out big money and let someone put there grubby paws all over your fine machine.

Yes ive completely drained the fuel tank and filled it up with new gas and it still ran like crap. The last thing i want to do is take it to a shop but i cant get it running and nobody can figure out whats wrong with it. Ive been trying to figure out the problem for four months and have had many people come over and try to fix it but nobody can.

[banzai510(hainz)]

have had many people come over

 

You didnt have me over!Did you ever ck the dizzy shaft for excesss wiggle? If the bushing is worn it could induce point bounce.

 

if you tried 2 different carbs already i would swap anothe point dizzy in.

 

 

this is simple we are just overlokking it.

[Bullet_theory]

have had many people come over

 

You didnt have me over!Did you ever ck the dizzy shaft for excesss wiggle? If the bushing is worn it could induce point bounce.

 

if you tried 2 different carbs already i would swap anothe point dizzy in.

 

 

this is simple we are just overlokking it.

 

 

nice... good call

 

oh.... side thought... when was the motor last rebuilt (rings and such) and is it burning oil? blue smoke? (just noticed that he said it starts up fine when its cold) does it have this same issue when the motor is still cold? or is it a constant thing?

[620connor]

have had many people come over

 

You didnt have me over!Did you ever ck the dizzy shaft for excesss wiggle? If the bushing is worn it could induce point bounce.

 

if you tried 2 different carbs already i would swap anothe point dizzy in.

 

 

this is simple we are just overlokking it.

The dizzy shaft does wiggle a little bit.. i guess i'll buy a new one and give it a try. Do you know where i could buy a new distributor for a 74 620? Thanks.

[620connor]

nice... good call

 

oh.... side thought... when was the motor last rebuilt (rings and such) and is it burning oil? blue smoke? (just noticed that he said it starts up fine when its cold) does it have this same issue when the motor is still cold? or is it a constant thing?

Its never been rebuilt, its bone stock from 74. It does burn oil, i have to add like half a quart of oil every two weeks. Its a constant thing, it runs like crap all the time.

[zed]

you say you have a new resistor - do you mean a ballast resistor to reduce voltage to the coil? Have you tried running it without the resistor?

You don't say if you tried a new condensor / capacitor? I have had new ones bad out the box. A bad condensor also makes a motor kick and miss. They are cheap - worth a try...

Have you done a compression check on this motor?

[banzai510(hainz)]

620Conner.

Side wiggle? You have to ask your self do you think its enough play to open up the points when driving.

As Im not there its all based on what you think. I hate for you to buy another dizzy and you get maybe a different one mthen it dont line up ect and your in a worse spot. Most us old datsun guys have these parts in the back yard where we can swap it in for a quick ck.

I also have to believe you have the correct coil and ballast resisitor in there. hate to find out you just grabed a coil from the junk yard and the 1st white ceramic resisitor you saw and in stalled it. I have to believe its the correct ohm value.

 

another thought is maybe remove the dizzy and just spin it to make sure the weights didnt explode in side and they are jamming up. But these are all simeple cks to a datsun guy that knows L motors.

[620connor]

you say you have a new resistor - do you mean a ballast resistor to reduce voltage to the coil? Have you tried running it without the resistor?

You don't say if you tried a new condensor / capacitor? I have had new ones bad out the box. A bad condensor also makes a motor kick and miss. They are cheap - worth a try...

Have you done a compression check on this motor?

Yes its a new L20B ballast resistor, yeah i tryed running it without the resistor but it still ran the same. I did install a new condenser, sorry i forgot to list that, ive tryed different points and condensers but got nothing. What does the capacitor do? i havent tryed that. Yeah i did a compression check, its making good compression.

[620connor]

620Conner.

Side wiggle? You have to ask your self do you think its enough play to open up the points when driving.

As Im not there its all based on what you think. I hate for you to buy another dizzy and you get maybe a different one mthen it dont line up ect and your in a worse spot. Most us old datsun guys have these parts in the back yard where we can swap it in for a quick ck.

I also have to believe you have the correct coil and ballast resisitor in there. hate to find out you just grabed a coil from the junk yard and the 1st white ceramic resisitor you saw and in stalled it. I have to believe its the correct ohm value.

 

another thought is maybe remove the dizzy and just spin it to make sure the weights didnt explode in side and they are jamming up. But these are all simeple cks to a datsun guy that knows L motors.

The dizzy wiggles a super super small amount.. i dont think it wiggles enough to cause any problems. The coil and ballast resisor are from an L20B so that should be fine on a L18 right? I'll remove the dizzy tomorrow and check to see if the magnets didnt explode, i didnt know that could happen.

[datzenmike]

It does sound like the primary jet getting plugged, but if you have a good fuel filter and brand new Weber, that isn't very likely.. however it is possible.

Have you checked the float bowl for water? It would be worth a try before you shell out big money and let someone put there grubby paws all over your fine machine.

It wasnt working before the swap, i installed the weber and it ran good for a while.. and then it started running worse than ever. Ive checked/done all of that stuff but no luck.

 

So you change the carb and it works for a while and then goes bad. Sounds like dirt or water in the gas. Take the carb off and clean it out... if it fixes the problem even temporarily that's it.

 

But when i give it full trottle the engine feels okay and has good power, but when i shift into the next gear there is a pause (like it almost dies) and then it slams me back in my seat and then the power feels good again as im still going full throttle. It does this through all 4 gears.

 

Sounds like a classic case of a blockage in the primary jet. Even worse on a carb that's too big.

 

 

 

I have a fuel regulator on it, i realized it was too big. Its set for the "100hp and under setting" so it should be fine.

 

It has number settings on it and only allows so much fuel to enter the carb depending on how i set it. Its set correctly.

 

The pressure regulator can't have an "under 100hp setting". It can only adjust the fuel pressure from the pump. Too high and it can force it's way past the float and needle and flood the carb. Find the 3 PSI setting and set it there.

[banzai510(hainz)]

I believe your dizzy is fine.coil ballast is fine if from a L20

go with datzenmikes troubleshooting.

[620connor]

Thanks for the help everyone!