hesitating when driving at 35-45 mph

[tfred1313]

i have a 1980 datsun 720. when im driving it starts to hesitate or jerk, but when i give it more gas it stops. any suggestions?

[fastboatman29212]

We need more info. Does it happen at all speeds? Inclines and down hills too? What style carb are you using? Stock carbs heavily rely on vacuum lines, and if they leak (old and cracked) then that might be a possible source of the problem.

For starters, I'd put a bottle of carb cleaner in half a tank of gas and run it until she's about empty to see if that helps clean out something in the carb.

Give us a bit more info if you can. Let us know what you've tried already.

[tfred1313]

its a new carb. it does it when im driving at a steady speed. vacum lines are good. i kinda think it has nothing to do with the fuel system but i could be wrong. thanks for the help

[fastboatman29212]

What kinda carb is it?

[flinterman2000]

its a new carb. it does it when im driving at a steady speed. vacum lines are good. i kinda think it has nothing to do with the fuel system but i could be wrong. thanks for the help

Did it do this before you changed the carb?

[tfred1313]

Stock carb, and ya it did it before. i checked the time and it was off 27 degrees. fixed that. that helped it but it still does it less frequently. i think i have a vacumm leak so ill fix that this weekend.

[PEZi]

awesome... keep us posted!

[flinterman2000]

Stock carb, and ya it did it before. i checked the time and it was off 27 degrees. fixed that. that helped it but it still does it less frequently. i think i have a vacumm leak so ill fix that this weekend.

Ever consider changing to a webber, or do you have emission test to do. Good luck with repairing your vacuum leak.

[tfred1313]

i live in cali. need all the smog crap.

[tfred1313]

Here is a couple of pictures of my truck... hope you guys like.

[flinterman2000]

Is that the L18 or L20B? Can't remember if the L20 is a cross flow head.

[tfred1313]

l20b.

[tfred1313]

I'm still waiting for a couple for gaskets to come in to see if i found the vacuum leak. then i need to get a new exhaust for her then get her smogged. hopefully next week she'll be running like new

[tfred1313]

well i got the gaskets... i put them on but i dont think i fixed the leak.. but i found the hesitation. it was the distributer cap. now i need to find the leak

[flinterman2000]

Keep trying. Hope you sort it out.

[current6]

I was having the same problem on my l20b. In the end it turned out to be the fuel filter that I installed inline before the pump. If you have a filter you might want to change it even if it doesn't look clogged.

[synack7350]

you can always get a cheapo spectre fuel pressure gauge for like 15bucks from auto zone and install it prior to the carb (but after filters and such it's always nice to be able to see what you are getting for pressure. they are so cheap I'm thinking of getting a second one to install prior to the filter so I can see diff pressure and know when its time to change the filter.