1968 Johnson 6hp hard starting and hesitation.

[baconbiscut]

Hello everyone, I got this motor as an evening project for after work and for when I'm not busy with school work. So far this is what I've done. I've rebuilt the carb with a carb kitf and used a parts cleaner tank to get things as clean as possible. I have also installed new coils, points, plugs, and condensers and I also installed a new fuel pump. I did reuse the old plug wires but they tested out fine. The issue i'm running into is once I get the engine started (5-6) pulls it runs very well, it idles well it accelerates fine, however if I leave it running at a set rpm for a few minutes and then try to accelerate the throttle quickly, it stumbles and dies. Most times I can save it and keep it running by feathering the throttle then slowly increasing it. After I do this the throttle response is decent until I let it idle for some time again. All while doing this the bulb on the fuel line stays hard, so I know the fuel pump is doing it's job. I also had the low speed jet set to 1 1/4 turn out from the start, I opened it up more but it didn't seem to make a huge difference it affected my idle but didn't remedy the issue.

Any ideas on where to go from here, would be awesome. I hate to take it to a shop and have them figure it out. That would ruin all the fun.

 

[racerone]

Compression test ?

 

[kbait]

Search 'link/sync'. Your carb's throttle butterfly may be opening too soon when you increase throttle, causing too much air and not enough fuel for the motor when increasing throttle from idle.

Good luck!

 

[baconbiscut]

Alright so I have the day off and I just got the motor in the barrel. I don't have a compression tester but harbor freight is right ujp the street I may go get one in a bit. The link/sync the throttle idea is interesting, what I found in the forums I didn't necessarily find to be helpful to my engine/situation. However, there is a tab underneath the magneto which moves the throttle plate as the timing is advanced. I adjusted this in, in various positions to delay throttle response and increase timing unitl it was adjusted all the way in. I believe that what I was doing was syncing the throttle, however i'm still running into the same issue with it dying out if the throttle is quickly advanced.

You'll have to forgive I'm a bicycle mechanic by trade, I can work on a 5000 dollar bike all day long, but I'm simply a novice when it comes to these engines, I have a fair amount of mechanical knowledge, but I also know that knowing and doing are too very different things.

 

[baconbiscut]

Bump

 

[undone]

The squeeze bulb shouldn't stay hard when it's running, it will get a little soft once the motor has been started, if it sucks flat there's a problem.

It could be the link & sync, Or could still be the carb or low compression, low compression can lead to hard starting and poor idle.

Try squeezing the bulb as you increase the RPM's, if this helps look for an air leak in the fuel lines, or possibly still a fuel pump issue.

 

[nwcove]

start your trouble shooting with a compression test, if the motor fails that.....you may want to rethink even bothering with it. if it has good compression, move on to ignition and make sure spark will jump 1/4" using a proper open air spark tester, if it passes that test move on to carb/fuel issues.

 

[Tim Frank]

start your trouble shooting with a compression test, if the motor fails that.....you may want to rethink even bothering with it.

^^^^^ +1.
It IS almost 50 years old and a quick tune-up may not be all that is required.

 

[thull]

I agree a compression test is in order because it can be a reason for hard starting and having to feather the throttle to keep it going. Cylinders should be within 10% of each other and preferably higher than 70. Do a search on here if you're not familiar with how to do it. Ground the plug wires so you don't risk ruining your new coils. Post back with the numbers after the test. Good luck!

 

[dude11]

At the start you said the low idle screw didn't have much affect..I bet your carb.isn't as clean as it should be.I chased a fuel problem on my 6hp.& after the 3rd. fail I ( out of spite) replaced the fuel pump..that fixed it.You may have what I did,,two or three things not completely failing but together was causing the tro.Back to the low idle screw,in order to really clean the passages,you should remove the alum.cap.I can never remember it's proper name.lol..That's where I'd start.

 

[Sandor27]

Did you replace the cork float with a modern plastic one? My guess is that you have a piece of cork in the bowl which is preventing you from being able to pull enough fuel when you need it to accelerate. So maybe when you run at one continuous RPM the debris gets stuck at the main high speed venturi pickup tube inlet but once you get her up to high rpm and drop back down it shifts to allow it to work. Anyway just a theory, but I'd put money on the carb not being 100% clean.

Also, did you replace the large washer at the high speed pickup tube? I once had a problem where this was not creating a seal and the engine would not run without choke on since it was not getting enough fuel.

 

[undone]

Did you replace the cork float with a modern plastic one? My guess is that you have a piece of cork in the bowl which is preventing you from being able to pull enough fuel when you need it to accelerate. So maybe when you run at one continuous RPM the debris gets stuck at the main high speed venturi pickup tube inlet but once you get her up to high rpm and drop back down it shifts to allow it to work. Anyway just a theory, but I'd put money on the carb not being 100% clean.

Also, did you replace the large washer at the high speed pickup tube? I once had a problem where this was not creating a seal and the engine would not run without choke on since it was not getting enough fuel.

I have three of these motors, and like you said, some tend to lose part of the floats and/or the cork washer on the main jet.

 

[Tim Frank]

OP has put what sounds like $100- plus in parts into an engine with unknown compression, and and is still fiddling with it....given that it is such an easy test, that does not make a lot of sense to me
But it's his money and time.....