Bronco 125 - header pipe red hot?

[mtraikov]

After troubleshooting with you alls help, today I had it running for about a minute or so, then I noticed the header pipe leading into the cylinder was red hot. Shut it off right away. Is it not getting enough fuel?

Also when i try to move the throttle, the motor dies. I’m assuming I need to adjust the fuel mixture screw? If so which direction is which?

On this carb, there are two screws on the chain side labeled in the diagram: “Stop screw for throttle” and “adjusting mixing screw”. Not sure of each of their functions.

Is there a choke/enricher on this carb?

Not sure which to adjust?

I’ve only had carbs on my old m900 for past experience.

[Duccout]

Hi,

The usual reason for excessive heat is a weak mixture and retarded ignition timing, and I suspect that you have something way out for the pipe to get that hot so quickly.


Colin

[graeme]

Agree with Colin,
Timing is too retarded.

Graeme

[IanHood]

Also when i try to move the throttle, the motor dies. I’m assuming I need to adjust the fuel mixture screw? If so which direction is which?

On this carb, there are two screws on the chain side labeled in the diagram: “Stop screw for throttle” and “adjusting mixing screw”. Not sure of each of their functions.

Is there a choke/enricher on this carb?

The “Stop screw for throttle” controls the speed of idle only, screwing it in will increase idle speed, screwing it out has the opposite effect. The “adjusting mixing screw” controls the fuel mixture at idle/low speed. Screw in for lean and screw out for richer mixture. I would be tempted to screw this in all the way (gently) and then screw out 1.5 to 2 turns as a starting point.

As for a "choke/enricher", I believe you have what is known as a 'tickler' - you should see a lightly spring loaded device that you can push down. For a cold engine you should be pushing this up and down maybe 5-10 times which has the effect of feeding more fuel into the carburettor float bowl for a richer staring mixture.

[mtraikov]

Any tech articles or posts on how to adjust the timing or checking the timing? Can this be done in a week?

[IanHood]

Any tech articles or posts on how to adjust the timing or checking the timing? Can this be done in a week?

I don't have any real experience with the Bronco engine but I would not be trying to play with the timing at this stage. As far as I can tell, altering the timing on a Bronco engine means pulling off the flywheel/rotor which probably requires a special tool. That makes me suspicious that the timing is out - I'm not even sure you can alter the ignition timing as this engine has a very basic set up with no dynamic advance. You should certainly adjust the points which, if they are way out, will have a small impact on timing. I THINK you adjust the points through a cutaway in the flywheel (http://www.oldtimerworkshop.com/files/Ducati_Bronco.pdf).

When you say the header pipe gets red hot, do you actually mean 'red' or just bloody hot (normal).

As for the the engine stopping when you move the throttle, that sounds like it is fuel related (e.g. blocked jet). It would certainly not be unusual for an carburettor that has been sitting around for some time to have a jet gummed up so you might want to pull it apart and inspect.

Ian

[ducwiz]

Any tech articles or posts on how to adjust the timing or checking the timing? Can this be done in a week?

How long it takes depends on your abilities and the tools you have available. Seems you have never done such job before.
You need

- a stroboscopic flashlight
- a degree wheel, with a mechanism to fix it on the crankshaft thread
- a corresponding pointer, attached to the engine at a convenoent screw.
- a piston stop tool, screwed into the spark plug's thread
- a felt pen

Using the stop tool and the degree wheel, find the crankshafts T.D.C. position, then leave the cranlshaft in this position. Now scribe a mark onto the outer surface of the flywheel, just in front of the pointer's tip. This is your T.D.C. mark
Rotate the flywheel into the fully advanced angular position (35-38° according to the manual), against the engine's rotating direction, and gain scribe 2 marks at 35 and 38° These are your fully retardes ignition angles.
Adjust the points gap to 0.3 - 0.4 mm. Access is gained through the oval holes in the flywheel (see manual).
Imho, you do not have to pull the flywheel when you want to adjust the ignition timing. The alternator/ignition base plate can be rotated on it's seat in the engine case, after the 2 corresponding mounting screws fixing the base plate are slightly loosened. It might be difficult to get good access to them with your screwdriver.
After the points adjustment, leave the pointing device attached to the engine, still giving you the reference for the timing adjustment. Now you can check the ign. timing with the stroboscope, after starting and revving the engine. Observe the marks for full advance and the reference pointer. If the pointer is not within the 35 and 38° marks at high rpms, adjust the timing by slightly rotating the alternator base, back or forth as needed.

cheers Hans

p.s. checking the valve timing could also clarify the red header, when the other adjustments (ignition, carb jetting, valve clearances) have been set to the correct values; maybe the timing gears on cam an crankshaft are misaligned by 1 tooth

[mtraikov]

Any tech articles or posts on how to adjust the timing or checking the timing? Can this be done in a week?

How long it takes depends on your abilities and the tools you have available. Seems you have never done such job before.
You need

- a stroboscopic flashlight
- a degree wheel, with a mechanism to fix it on the crankshaft thread
- a corresponding pointer, attached to the engine at a convenoent screw.
- a piston stop tool, screwed into the spark plug's thread
- a felt pen

Using the stop tool and the degree wheel, find the crankshafts T.D.C. position, then leave the cranlshaft in this position. Now scribe a mark onto the outer surface of the flywheel, just in front of the pointer's tip. This is your T.D.C. mark
Rotate the flywheel into the fully advanced angular position (35-38° according to the manual), against the engine's rotating direction, and gain scribe 2 marks at 35 and 38° These are your fully retardes ignition angles.
Adjust the points gap to 0.3 - 0.4 mm. Access is gained through the oval holes in the flywheel (see manual).
Imho, you do not have to pull the flywheel when you want to adjust the ignition timing. The alternator/ignition base plate can be rotated on it's seat in the engine case, after the 2 corresponding mounting screws fixing the base plate are slightly loosened. It might be difficult to get good access to them with your screwdriver.
After the points adjustment, leave the pointing device attached to the engine, still giving you the reference for the timing adjustment. Now you can check the ign. timing with the stroboscope, after starting and revving the engine. Observe the marks for full advance and the reference pointer. If the pointer is not within the 35 and 38° marks at high rpms, adjust the timing by slightly rotating the alternator base, back or forth as needed.

cheers Hans

p.s. checking the valve timing could also clarify the red header, when the other adjustments (ignition, carb jetting, valve clearances) have been set to the correct values; maybe the timing gears on cam an crankshaft are misaligned by 1 tooth

Hans - so to put it simply, adjusting the timing is rotating the base plate that holds the coils/points/condenser? I saw reference marks on the base plate and the engine. When I took the flywheel off I noticed they weren’t aligned so I aligned them. Should I orient it back to the position I found it in? I’m confused why that would affect timing because the plate is fixed to the engine with screws like you said.

Also - how do you measure the gap of the points? There is a screw that rotates/moves the points, but what is the reference point?

Thank you,

Mike

[Jordan]

Some info here:
http://hogervorst.tech/ducati-online-ma ... ations.pdf

[mtraikov]

That is an excellent resource! Thank you Jordan.

I’m having a hard time finding a degree wheel online? Can anyone point me in the right direction?

Is this what I’m looking for in terms of stroboscopic flashlight?
Innova 3568 Digital Timing Light https://a.co/d/0ubSPHH

And what is a corresponding pointer? What is the thread size for the piston block?

Just so I’m understanding - adjusting the ignition timing is rotating the entire base plate that is mounted to the engine. Adjusting the points gap is the the little flathead screw next to the points. The gap is between the crankshaft and the fiber block of the contact breaker? How can I measure this accurately?

What should I use to lubricate the lubricating felt?