Marvel MA4SPA Carb. Problem?

[n40ff]

If it ain't broke, don't fix it.

I just had to "fix" it....now it seems to be broke, maybe?

Well, it didn't seem to be broke but now I don't know?

Finished the annual on my Tu-holer and while it was apart I decided to weld a bracket to hold the end of the Throttle cable in the front pit Like I had made for the Acroduster. Throttle was working fine and as I did the inspection I found it was fully closing and opening but I wasn't happy with the clamps I had holding the cable end.

As I continued to work on it checking travel It started being very hard to open....... I spent all day on this thing.... I did weld on the new bracket and figured it would be the fix but it wasn't.

I found that it was the accelerator pump that was causing the issue. After the throttle is cycled a couple times the pump seems to "load up" and it is VERY hard to push the throttle to full open. Is this normal? If so, it seems I don't understand how this thing works?

Again, it was working fine. The carb was working fine on this engine in my EAA bipe but I had it rebuilt with new float when I put it on the Spezio. It now has 55 hours on it since rebuild.

Again, if I push the throttle slowly it will open but the accelerator pump gives high resistance toward the end of travel.

Don't know if it's broke or not? I have not run it, I wanted to "run" it by you guys before I put the cowl back on. If it is not normal, what's wrong and how to fix?

Thanks,

Jack

 

[Aviator]

I'm not a carb man, but the symptoms you describe suggest some sort of hydraulic lock. Maybe a blocked checked valve?
www.insightavionics.com/pdf files/MA-4 Carb Manual.pdf p.19

 

[n40ff]

Aviator,

Thanks. I found that manual yesterday and pondered it......I admit I'm not a carb man either. I went ahead and put the cowl back on and started it. Everything seemed normal/as it has been. Flew it and again was normal.

That said, I pulled the cowl and I think will look into it some more.

Meanwhile I finally got everything repaired on the Acroduster's IO320, rolled it out, warmed it up and checked the static rpm which was ok. Been several months getting that done. I hate winter!


Thanks again,

Jack