Flat spot in acceleration

[olive]

I have been tinkering around with my 78 fj40 for a while now and have got all the mechanical gremlins out except for one last one, there is a flat spot in the acceleration from about 40-50mph. I've desmogged the engine and added a trollhole carb so now I'm down to the distributor. It's a stock dizzy and the last thing I think could be causing this problem. Has anyone ever changed the springs and weights in these? Is there a kit out there for this? Would I be better off letting an expert handle this kind of job? Any help would be appreciated

 

[wngrog]

Mine started doing that and it was just a fuel filter.........

 

[tyama]

hiya, throw in a petronix pointless kit for the dizzy if it's not the fuel filter. You'll be glad you did. It's one of the better upgrades I did on my rigs.
best, ty

 

[Pin_Head]

More detail would help, like what gear and what RPM? Full throttle, partial throttled?

Make sure that the centrifugal advance works and is not sticking.

Check that the vacuum secondary is kicking in. It might need to open earlier. Is the primary opening all the way?

 

[olive]

Thanks for the reply's, I think I'll start with the simple thing (fuel filter) first. As for the flat spot it's in every gear near the mid- upper RPM range and it doesn't seem to matter if its full or part throttle. Once I hit about 50mph it just goes away and cruises great down the highway. Defiantly looking into the petronix conversion, that looks just to be a good upgrade regardless.

 

[Pin_Head]

It is not misfiring, so changing the ignitor is a waste of money and time. The stock 78 ignitor is great.

Since it doesn't matter what the throttle position is and it happens at the same RPM, sounds like the centrifugal advance may be sticking.

 

[olive]

Never messed with a centrifugal advance mechanism is it able to be lubricated? I've had the top of the distributor apart to check for rust on the weights and springs and they were all clean. Would silicone spray work good enough?

 

[Pin_Head]

I don't know about silicon, but some spray lube sounds like a good idea.

 

[olive]

After work today I got into the distributor to check the springs/weights and noticed one spring(the longer of the two) was quite loose, almost to the point of falling off. Could this be part of the problem or is it just a normal wear piece? Does anyone sell new springs? can I get lighter springs. I see that SOR sells used springs for a 78 but I'd just as soon buy new. Would a lighter spring help with the desmog I did on the engine??

 

[Pin_Head]

They should be the same length and same strength. Replace.

 

[olive]

I know I'm asking a lot but is there a vendor here on MUD that you would use for these parts? I've looked at my local parts stores and come up with nothing and would really like a reliable parts source....

 

[65swb45]

Logically, how could a distributor that is not working properly at midrange start working better at higher rpm? Doesn't sound right to me.

I'd be interested to know what vacuum you're pulling at midrange stumble and at high speed 'smooth '.

 

[Pin_Head]

Sometimes the centrifugal advance has a rough spot in the middle of its range and sticks there when it should continue to advance until the RPM comes up and the force overcomes the roughness and let's it advance to where it needs to be. In other words, the advance curve has a flat spot.

 

[olive]

I am looking for some springs for the distibutor but the only ones I've found so far are the used ones from SOR. If anybody knows where I can pick up a new set I'd appreciate the info, Thanks to all that helped me out.

 

[Weber Sarge]

Start hunting for a distributor shop or check with the local engine rebuilders . As long as you match length , number of winds and wire diameter it should be the same . Another culprit could be the fuel level in the carb - make certain it's in the center of the window , too low and it can cause flat spots in the mains .

Sarge

 

[FJ40Jim]

The dissy springs have been discontinued for 15yrs now.
FWIW, the springs are not the problem, they don't wear appreciably or fail.

 

[olive]

Well I know for sure it's the distributor....since I couln't find any replacement springs I took the one that was so long it literally fell off when I went to grab it with some needle nose pliers and decided to shorten it up to the same length as the other(by just rebending the hook at one end) and man does it run like crap now! Flat just about all the time feels like it's not getting any fuel but I only changed one thing so I guess the hunt is on for a new distributor because I can't seem to bring myself to fork out $40 for a set of used springs....yet.

 

[FJ40Jim]

I'll sell you a pair of good used springs for $20, if it will make you feel better to replace them.

 

[cruiserdan]

As an additional footnote ignitors either work or they don't. They do not "sorta work".

 

[rkymtnflyfisher]

There is a serious "gold medal Olympic team" giving you the best info you could ask for.

There is a guy who has commented that can solve all your problems. Send your dizzy in and get it rebuilt.