Hodgson Radial - won't run

[Jon James]

I need help.

I have completed buiding the Hodgson 9 cyl radial. Terry Mayhugh's thread was tremendous help. Unfortunately, mine barely runs. I will go over the basics I have:
1. Using Perry 4600 carb, as recommended by Lee Hodgson.
2. S/S CDI ignition.
3. Compression is fair at 50 - 60 PSI.
4. Valve timing has been checked and rechecked.
5. Ignition timing 10 Deg advance.
6. Oil flow is controlled.
7. Engine is getting fuel.
8. Spark is strong. Plug gap at .020". NGK CM6 spark plugs.
9. No air leaks. I pressurized intake system to verify.
10. I have tried gasoline and camp fuel.

When it does run, it hits on only 4 or 5 cylinders. Not always the same cylinders on different runs.

I am at the end of my rope on this. Any help would be greatly appreciated.

Regards,
Jon

 

[Longboy]

I have had four cylinders run on three till I fine tune the carb needle till that last cylinder starts burning after previously removing plugs and blowing the fuel flood off the electrodes.

 

[WOB]

Check your distributor and plug wires. You might be getting crossfiring inside the cap. The wires should not run bunched in parallel for any distance. The distributor is barely big enough to work properly when all is correct. Expect malfunction if something is not right.

WOB

 

[Longboy]

Pull the plugs on the dead cylinders and run engine. Add a plug and wire one at a time. If remaining dead on those cylinders, review spark and fuel to that or those remaining inactive. Random and not consistent/ same cylinders not active.......I'd head over to the spark distribution. Can you trouble shoot a radial with a flywheel instead of a prop on?

 

[JP2]

My experience was very similar in getting my H9 to run.

The change that made all the difference was moving to a smaller carburetor. I switched to a Traxxas 4033. I also have the 4600 carb but I think it is too large. I was never able to get my engine to run on the 4600. I switched back to it after everything was working and I couldn't get the engine to start.

After switching the carb and getting the engine to run consistently I had to modify the rotor tab to reduce its size to keep the cross fire under control.

John

 

[Jon James]

My experience was very similar in getting my H9 to run.

The change that made all the difference was moving to a smaller carburetor. I switched to a Traxxas 4033. I also have the 4600 carb but I think it is too large. I was never able to get my engine to run on the 4600. I switched back to it after everything was working and I couldn't get the engine to start.

After switching the carb and getting the engine to run consistently I had to modify the rotor tab to reduce its size to keep the cross fire under control.

John

This sounds exactly like my problem(s). I have done the same with my rotor. Sometimes I think the S/S ignition is too hot. I just ordered the Traxxas carb. Hope it works.
Thank you very much for your advice.

Jon

 

[JP2]

The S/S ignition will jump a spark through surprising places.

I gave myself a weeks worth of head scratching with the ignition. I had completed and tested the distributor at least 9 or 10 months before attempting to start the engine. On the first attempts to start it, my plugs wouldn't fire consistently. All of the plugs would fire, but only about every 2nd or 3rd firing rotation. Like you, I checked and checked, even replacing the ignition module with another one I had on another engine. Same behavior. I thought maybe the box of plugs I had were defective so I bought another box. Nothing helped. I decided I had something fundamentally wrong with the distributor and needed to tear it down. When I removed the cap and rotor I noticed a burn mark on the top of the distributor shaft. At that moment, I realized (remembered) exactly what what happening. When I was drilling the rotor tab mounting holes, the quill handle slipped and I drilled one of the holes completely through the rotor. Instead of using my last piece Acetal to make a new rotor, I used epoxy to fill the hole. Well, as you can guess, my epoxy fix must have had a micro sized hole and the ignition was more than capable of firing through it into the distributor shaft.

You're close and the result is very rewarding.

John

 

[stevehuckss396]

If you suspect an ignition problem try checking your sparkplug gap. Try gapping the plugs at around .015 and see if that makes any improvement. With the smaller gap you increase your chances the spark will make it to the plug instead of jumping around in the cap. I run my v8 at .012 and it helps out a bunch. I also like the suggestion to reduce the size of the carb. You can always go back up after getting a good idle and some throttle response.

 

[Jon James]

The S/S ignition will jump a spark through surprising places.

I gave myself a weeks worth of head scratching with the ignition. I had completed and tested the distributor at least 9 or 10 months before attempting to start the engine. On the first attempts to start it, my plugs wouldn't fire consistently. All of the plugs would fire, but only about every 2nd or 3rd firing rotation. Like you, I checked and checked, even replacing the ignition module with another one I had on another engine. Same behavior. I thought maybe the box of plugs I had were defective so I bought another box. Nothing helped. I decided I had something fundamentally wrong with the distributor and needed to tear it down. When I removed the cap and rotor I noticed a burn mark on the top of the distributor shaft. At that moment, I realized (remembered) exactly what what happening. When I was drilling the rotor tab mounting holes, the quill handle slipped and I drilled one of the holes completely through the rotor. Instead of using my last piece Acetal to make a new rotor, I used epoxy to fill the hole. Well, as you can guess, my epoxy fix must have had a micro sized hole and the ignition was more than capable of firing through it into the distributor shaft.

You're close and the result is very rewarding.

John

I also had the same problem with the rotor. I removed the screws and glued the contact to the top of the rotor. On the bench I connected the High tension lead to the rotor contact and a 3/8" rod in the shaft hole, and the spark jumped right through. That's passing through .175" of acetal!
I replaced the brass tab with a piece of printed circuit board. I believe that stopped that short. I'm still not confident about the distributor cap.

I am going to wait until I get the Traxxas carb before I go further.

Jon

 

[Jon James]

If you suspect an ignition problem try checking your sparkplug gap. Try gapping the plugs at around .015 and see if that makes any improvement. With the smaller gap you increase your chances the spark will make it to the plug instead of jumping around in the cap. I run my v8 at .012 and it helps out a bunch. I also like the suggestion to reduce the size of the carb. You can always go back up after getting a good idle and some throttle response.

I have also tried a reduced gap, it seemed to help a little. I will wait until I get the Traxxas carb before I go on.

Thanks
Jon

 

[peterl95124]

I learned from a very wise engine builder to always make the first distributor for an engine out of highly polished clear acrylic, that way you can see if it is cross firing. See through also helps immensely with getting the timing right. Since then I've never replaced any of my distributors with delrin, the see through acrylic just looks too cool.

 

[rsholl]

Steve is correct on the plug gap of .015" and yes my CDI functions different than the old Kettering system. I have talked with Lee about some of the issues encountered with the distributor set up. First, we do not need the brass tower contacts protruding down the inside of the cap. This leads to sparks jumping down to the base of the distributor sometimes. Second, the rotor contact is way too wide. It only needs to be a strip about the width of the brass contact in the towers. If you can't get the spark through the distributor, the engine will never run smoothly. I have worked on several of these engines and my last test is with my little doughnut spark tester between the end of the spark plug wire and the spark plug. Turning the engine over slowly by hand and moving the tester from plug to plug in the firing order you should get a spark through the tester. I normally set the gap in the tester at no more than .010- .015. Once the spark gets through the tester it means the distributor is good to go. One more thing that can help. The CDI will function on 4.2 volts so you may have better luck with only 3 cells. This will reduce the output of the CDI and normally it will have much less tendency to jump a spark places it shouldn't. Lots of good advice from members and I see they have had many of the same problems I have dealt with in the past.

 

[Jon James]

Steve is correct on the plug gap of .015" and yes my CDI functions different than the old Kettering system. I have talked with Lee about some of the issues encountered with the distributor set up. First, we do not need the brass tower contacts protruding down the inside of the cap. This leads to sparks jumping down to the base of the distributor sometimes. Second, the rotor contact is way too wide. It only needs to be a strip about the width of the brass contact in the towers. If you can't get the spark through the distributor, the engine will never run smoothly. I have worked on several of these engines and my last test is with my little doughnut spark tester between the end of the spark plug wire and the spark plug. Turning the engine over slowly by hand and moving the tester from plug to plug in the firing order you should get a spark through the tester. I normally set the gap in the tester at no more than .010- .015. Once the spark gets through the tester it means the distributor is good to go. One more thing that can help. The CDI will function on 4.2 volts so you may have better luck with only 3 cells. This will reduce the output of the CDI and normally it will have much less tendency to jump a spark places it shouldn't. Lots of good advice from members and I see they have had many of the same problems I have dealt with in the past.

Thanks to all of you for your expert advice.
Jon

 

[Longboy]

The S/S ignition will jump a spark through surprising places.

When I was drilling the rotor tab mounting holes, the quill handle slipped and I drilled one of the holes completely through the rotor. .................. Well, as you can guess, my epoxy fix must have had a micro sized hole and the ignition was more than capable of firing through it into the distributor shaft.

You're close and the result is very rewarding.

John

Been there too, points ignition. I ignored it and my engine ran erratically and stalled. 4-40 threaded hole for the brass tab on the top and a 3/16 in rotor shaft hole that passed through. Coil energy just grounds into the shaft. Remade the part and was rewarded with normal operation.

 

[Jon James]

Steve is correct on the plug gap of .015" and yes my CDI functions different than the old Kettering system. I have talked with Lee about some of the issues encountered with the distributor set up. First, we do not need the brass tower contacts protruding down the inside of the cap. This leads to sparks jumping down to the base of the distributor sometimes. Second, the rotor contact is way too wide. It only needs to be a strip about the width of the brass contact in the towers. If you can't get the spark through the distributor, the engine will never run smoothly. I have worked on several of these engines and my last test is with my little doughnut spark tester between the end of the spark plug wire and the spark plug. Turning the engine over slowly by hand and moving the tester from plug to plug in the firing order you should get a spark through the tester. I normally set the gap in the tester at no more than .010- .015. Once the spark gets through the tester it means the distributor is good to go. One more thing that can help. The CDI will function on 4.2 volts so you may have better luck with only 3 cells. This will reduce the output of the CDI and normally it will have much less tendency to jump a spark places it shouldn't. Lots of good advice from members and I see they have had many of the same problems I have dealt with in the past.

Hi Roy,
Thanks for your advice. We have talked on the phone a couple times recently.
Regarding batteries, I have your 4 cell battery pack. If I remove one battery, do I need to put a jumper in place of the battery?

Thanks,
Jon

 

[rsholl]

Jon, the easiest way to jumper a cell is to cut a piece of AL or brass the length of a cell and put it in place of the removed battery. 1/2" stock works good for the dummy cell. You may need to bevel one end, just make sure it is making contact with box connectors. Quick check with a volt meter will confirm. Back to the distributor. On one of the engines I worked on that I was sure was distributor issues, I fabricated a plate out of 1/8" flat PVC. I can't seem to find it or I would post a picture. The plate was basically the shape of the distributor base outline which I drilled the 10 holes that would have been in the cap. I installed #2-56 screws and nuts. I sat it on top of the distributor (screw heads down) and measured from the ears on the plate to the ears on the distributor base. I add about .010" to that dimension and made 2 round stand offs. When the plate is mounted on the stand offs, the rotor should clear the screw heads. Remount the all the spark plug wires (with extra nuts) and you will easily be able to see where the spark is going. With the engine running you should see a nice smooth spark rotating around the inside of the plate. If any are jumping (very doubtful) it is easy to see. That plate basically eliminated any where the spark could go except to the spark plugs. This is providing you have made the smaller rotor contact. With the original contact you can see sparks jump off the back corners of that large contact. You are close Jon, a little TLC will get you up to speed.

 

[mayhugh1]

If your problem really is the distributor, and if the engine runs OK but peters out after several seconds, then it's possible that ozone is collecting inside the enclosed space. Once this happens, the atmosphere inside becomes a 'glow lamp'. This was a problem for some hot rodders back in the 'good old' days who converted their stock ignitions over to CDI's. MSD told them to drill a few holes in top of the distributor to vent it. The ozone is also corrosive, and many were also seeing the insides of their distributors also 'rusting.' The advise was the same - drill some holes in the top of the distributor. Many refused to do this because it seemed counterintuitive since they thought it would allow moisture inside.

Roy's advice on the distributor mods is sound. I designed my own distributors to avoid those very same problems when I built my two radials. The details can be found in their build threads on this forum. Much of what I do was lifted from Jerry Howell's V-4 distributor which I consider an excellent design.

The thing is, though, if it is a distributor problem, I would expect you to also be blowing Hall devices left and right, unless I missed the fact that you're using points. - Terry

 

[Jon James]

Thank you Terry for your advice.

I benefited greatly from your radial build thread.
Regards,

Jon

 

[Jon James]

Jon, the easiest way to jumper a cell is to cut a piece of AL or brass the length of a cell and put it in place of the removed battery. 1/2" stock works good for the dummy cell. You may need to bevel one end, just make sure it is making contact with box connectors. Quick check with a volt meter will confirm. Back to the distributor. On one of the engines I worked on that I was sure was distributor issues, I fabricated a plate out of 1/8" flat PVC. I can't seem to find it or I would post a picture. The plate was basically the shape of the distributor base outline which I drilled the 10 holes that would have been in the cap. I installed #2-56 screws and nuts. I sat it on top of the distributor (screw heads down) and measured from the ears on the plate to the ears on the distributor base. I add about .010" to that dimension and made 2 round stand offs. When the plate is mounted on the stand offs, the rotor should clear the screw heads. Remount the all the spark plug wires (with extra nuts) and you will easily be able to see where the spark is going. With the engine running you should see a nice smooth spark rotating around the inside of the plate. If any are jumping (very doubtful) it is easy to see. That plate basically eliminated any where the spark could go except to the spark plugs. This is providing you have made the smaller rotor contact. With the original contact you can see sparks jump off the back corners of that large contact. You are close Jon, a little TLC will get you up to speed.

Roy,

Thanks so much. I really like your visible distributor idea.

I am on hold right now, waiting for a smaller carb, as advised earlier in this thread.
Regards,
Jon

 

[WOB]

Two things. When I built my Hodgson 9 Hall effect distributor(S/S CDI, 1/4-32 Rimfire plugs) I used nylon screws to hold the rotor contact(full width) to the rotor body. Seemed to me to be some insurance against unwanted arcing, but maybe wishful thinking. For a carb, I used the carb from an O.S. FT-300 engine. It has an 8 mm bore. The engine ran well from the start once I got the carb adjusted and with no apparent ignition problems .

WOB