’78 International Scout II – Part 4b Fuel and Air Delivery

In carburetor, international harvester, project truck, scout, timing on January 11, 2015 at 5:10 am

A few days later the new carburetor was here.  It actually arrived a day early.  Thank you  It sat for another day and then I got it bolted onto the Scout.  Now comes the most embarrassing part of the entire saga.  At this point the truck had sat a few more days without a carburetor and so the fuel line sat without being attached to anything.  Any fuel in the line had either evaporated or spilled out.  When I hooked it back up and attempted to start the Scout I wasn’t getting any fuel. I tried just letting it sit for a while with the fuel pump running.  No luck.  I tried attempting to suck on the pipe to pull fuel up.  I went to the gas station filled my little gas can and poured gas down the line.  The truck ran for about 2 seconds.  At this point I decided that maybe the pump was just having problems pulling the fuel up it’s level.  I had read somewhere that some fuel pumps were good at pushing full and some good at pulling fuel.  This one was mounted high up on the inner fender well of the Scout.  So the heavy lifting so to speak was pulling fuel up.  I decided that I should move it down to the frame so that it wouldn’t have to pull fuel.  I would have to push the fuel uphill instead.  The first problem I ran into was that I didn’t have any threaded holes on the frame to use.  I don’t have any taps to thread holes myself and the frame is completely boxed in so I can’t use a nut on the back side.   I decided I would mount it to the bottom of the cab instead.  Just where the passenger foot well starts to turn up to be exact.  I got everything done and turned the key to activate the fuel pump.  Nothing.  I could hear it gurgling a little bit but no fuel came up the pipe.  I gave up and decided I would pour the reaming fuel in my gas can into the the tank so that it would be a little harder for somebody to steal it.  After pouring the first gallon or so, fuel started to come out of the fuel line.  Three hours of fighting and working this problem and it turns out the truck was just out of gas.  At some point I REALLY need to drop the gas tank and fix the fuel sender so the gas gauge will work.

After screwing the fuel line back into the carburetor the truck started right up.  And then promptly died again.  I tried a few times.  Same result.  I slept on the problem.  I decided that maybe the vacuum plug we talked about earlier was just a bit too knackered and should probably be replaced.  Vacuum leaks are a big problem with carb tuning so this seemed like the place to start.  After replacing that plug the truck would start and run.  I celebrated by driving the truck to the gas station and then on to the parts store to pick up a timing light.  I still didn’t know how to use it, but knew I would need one.

By this point I had learned a bit more and knew where the actual idle adjustment screw was and that what I had used before are fuel/air mixture screws.

Scout Old Carb (6)

In the bottom right of this photo, just above the black covered throttle cable you will see a screw with a spring on it.  This is the idle adjustment screw.  It screws in to push the throttle level over.  The screw above that helps adjust the throttle on cold start up somehow.  I still haven’t figured that out, but need to as one of the current problems now is cold starting.  Adjusting both the idle screw and the mixture screws I was able to get the idle adjustment down to about 1300ish but the Scout would die no matter what I did to get it lower.  All this work and I wasn’t doing any better than I had with the old carburetor.  Now I guessed that the problem probably had something to do with timing so I busted out that timing light.  I had watched some YouTube videos (thank you Hot Rod magazine) and now knew about the timing reference marks.  I crawled under the truck to find the mark on the harmonic balancer.  It was just an engraved line that was very hard to see with all the grease and oil down there.  I cleaned it up and painted the line white to make it a little more visible.

I haven’t been wasting my time and by this point I had learned a little bit more about timing as well.  The spark plug is supposed to fire a little bit before the piston gets to the top of the cylinder.  This gives the spark time to start the explosion of fuel and air so that it is at it’s strongest just as the piston gets to the top.  This takes a set amount of time depending on spark plug and the fuel/air mixture.  However as engine rpm goes up it takes less time for the piston to travel up the cylinder.  So at higher rpm the spark must fire earlier in the cycle to get the explosion to happen at the correct piston position.  There are some springs inside the distributor that allow it to advance the timing (fire the spark earlier) as engine rpm go up.  By swapping out those springs you can change how fast it will advance and the total amount of range (from the idle rpm timing to the high rpm timing) that the distributor is capable of.  My shop manual only lists the initial timing which is 10 degrees of advance timing.  I have no experience with this but knew that at 1300 rpm the timing should be more advanced than the 10 degrees that it needed at 650 rpm.  So I guessed.  I was able to get the idle rpm down to 1100 but it would go no lower.

I called a friend and while talking to him we decided that the second vacuum port I had mentioned earlier probably also needed to be capped.  Luckily I had bought a variety pack of vacuum plugs so I had one that was the correct size.  (In a completely unrelated note I really have a hard time spelling vacuum.  I keep trying to spell it vaccum instead of vacuum.  Hurray for spell check.)  That did it.  I was able to get the curb idle rpm down to 675.  It still smelled like it was running rich, but I was happy to declare victory for the day and do something else.

Today I got back after it.  I discovered that my timing guess was way off.  At 675 my timing was exactly at TDC.  I advanced it forward 10 degrees.  At this point I cleaned up the tab with the reference marks and painted the reference line white as well.  I still don’t know what the timing curve should look like but I do know what it is supposed to be at idle so I will just have to be happy with it and hope that the distributor has the correct springs installed.  I also tried to lean it out by increasing the throttle using the idle screw and decreasing the fuel mixture. I’ve had mixed success.  Right now it idles right around 800, maybe a touch less.  It isn’t burning rich anymore though.  Granted this is only a nose test.  I don’t smell fuel while it is running.  I don’t have the emissions testing equipment to tune this completely.  But I have it at the lowest mixture and idle speed that I have been able to achieve without the motor dieing.  800 is still a little bit high, but this engine needs all new gaskets.  I expect that there are other vacuum leaks and assorted issues that I will be able to address as work continues that will ultimately allow the motor to run smoothly and dependably at 650-675 rpm.  I ended the day with another victory lap of the neighborhood.

Getting through my issues with the carburetor and the timing required the most amount learning that I have had to do yet while working on the truck.  I spent a fair amount of time reading the manuals, message boards, and watching YouTube videos.  The frustration has been high on occasion but so has the sense of accomplishment when I learn something else and overcome my problems even if it is only in small increments.  This was the point of the project all along.

I had planned on attempting to build a rear bumper for the Scout with my cousin tomorrow.  Right now I think that is probably getting ahead of myself though.  Instead I think we will work on sorting out the electrical gremlins and getting the dash reassembled and the final seat belt installed. (I bought a new one for the front passenger today.)  If there is time after that and another victory lap, I want to start taking apart the cooling system.  I need a new radiator.  The one I have had a pretty good leak.  I put some stop leak stuff in and that seems to have stopped it for now.  This is only a short term fix though.  It needs a new radiator.  I need to check the radiator for the transmission cooler as well as remove some final components of the factory air conditioning.  AC on a topless truck doesn’t make much sense.  It didn’t work anyway so I have slowly been removing it.  I would like to get the water pump removed as well.  It leaks as well.  I have ordered a new gasket for it.  It won’t be here for a few days but if I can get help getting everything removed it will be much easier.  This will give me a chance to get the front of the motor cleaned up as well.  Ultimately all the gaskets need to be replaced but if I can get the motor cleaned up that should show me where any leaks are so that I can prioritize future projects.  That’s the current plan.  I’m not sure how much I will get through tomorrow but I’ll let you know in the next installation of this project blog.


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