doodlebug throttle linkage?

[chazdaddy]

I have new to me dirtbug. I have been working on it and it's running pretty well. Seems to be about as fast as my Murray Track 2 with 3.5hp Tecumseh, that is running very well.

Today, I put a tach on the dirtbug engine to check the governor. Governor was working, but way too high. Max rpm was 5220, freewheeling it would go past 5000 and the governor would pull it back to 4900. I had no idea engine was turning that fast. :doah:

Looking at the throttle linkage, I think I am missing the adjustment that limits the throttle opening (the adjustment for small kids to limit throttle to less than full throttle). On my bike, there is nothing to limit the throttle opening. The effect is the governor spring is pulling on the governor arm harder, takes more rpms for the the governor to overcome the spring and close the throttle. I don't think anyone changed anything, I think a part(s) just fell-off from vibration.

What to do to fix it? Can someone post a picture of a complete throttle linkage, so I see what it's supposed to look like? Any ideas where to get this part? :shrug:

 

[Dudlydoodleright]

You will note that the throttle linkage is connected to the governor arm by a spring. On the governor arm is 3 holes and the linkage 2 holes. To reduce the RPM limit move the spring to the lower holes and to increase the RPM setting move it up. 5200 RPMs while riding is about as fast as the motor will turn unless the exhaust is modded as by that speed the exhaust will start to back flow durring overlap--so lower the spring-you have a total of 5 other settings and if your a few hundred over 3600 the motor will take it.

 

[creia]

What type/brand of tach are you using?

 

[Clayon]

Ya if your 2.8hp on your db30 is revving 5000 that means the gov must be bypassed cuz I think that they rev under 3000 stock. That would also explain why it would be about as fast as your Murray. I have blown up a 2.8hp by taking the gov off, make sure it is actually on, I thought I had pics of the linkage but the ones I hav are after I removed the gov sorry. :thumbsup:

 

[chazdaddy]

Thanks for replies. After I posted, I looked at the throttle linkage some more and found where the throttle stop screw is, no parts missing. The throttle stop screw was backed all the way out.

The governor is working, but with the throttle stop backed all the way out the governor doesn't kick-in until approx 5000 rpms. I turned it in and the effect is dramatic on the spring pressure. I haven't tested it yet, but I am sure this will lower the governor setting.

Now I know why these engines are blowing even with the governor still installed. I know most out there do not have a tach and are assuming the engine can only turn 3600 rpms if the governor is still installed, wrong!

I used a Digatron instrument off a kart to check rpms. It's a very good instrument, very accurate, I have no doubts about the rpms. I will do some more testing and report back early next week.

 

[Dudlydoodleright]

I use a knock off of a Yamaha boat motor hour/tach--I think the one I have is too cheap and next time I'm getting a real Yamaha. The setting I run gives RPM and on shut off, hours-helps me with how far I can go out before I have to turn back. It also lets me know it's time for oil change, chain clean and lube, and clutch clean and lube. The Hour/tachs are on e-bay but the el-cheapo I bought tells me get a Yamaha! look around and you'll find they are only a little more in price than a cheap one.
The DB"s govenor can be mis-set that is why it has 6 settings --stock is middle hole on the govenor arm and the lower hole on the linkage side--but the spring can be bent and that will change it too. Start middle on arm and lower on linkage-then dial it in from their.

 

[chazdaddy]

OK, I didn't use the tach, wasn't necessary. I turned in the throttle control screw that limits how much you can turn the throttle grip on the handlebars.

I turned it several turns, maybe 6 or 8. Took it for a test ride, was really slow, would be perfect for 5 year old. Then I turned it out 2 turns and tested it, was a little faster. Turned out this screw 2 more times 2 turns each time, and each run was faster.

Notice I didn't do anything with the springs, such as change which hole they were hooked to, or shorten them, or stretch them. All I did was change the setting of the throttle control screw.

Conclusion: (1) my minibike governor is working properly, (2) if you turn the throttle control screw out too much, this engine can turn too many rpms with the governor installed (with tall gearing, light rider, or freewheeling), (3) without the governor installed, engine will turn enough rpms to float the valves, throw a rod, or explode the flywheel, but I didn't test for that and don't intend to, and (4) great little engine for what it is IMO