Demon 500 CFM rebuild questions

[tgell001]

So I just rebuilt my demon 500 cfm for my 2010 Volvo penta 3.0L and it actually went really well first try. Problem is the rebuild kit came with a 30CC accelerator pump and the stock one was a 50CC. I've got the lever arm adjusted so that the 30CC works fine (e.g. moved the cam up to the closest of the 3 holes).

Question is... obviously there was a reason that it came from the factory with the 50cc. Is there going to be any serious issues with running the 30cc? if so I think the 50cc that I removed is still fine. It doesn't look torn or cracked at all (but symptoms of the reason for the rebuild pointed at the accel pump but could have been something completely different)

Also, Volvo freaking painted over the sight glass on the bowl (among everythign else) to adjust the float , aside from scrapping paint until I can see is there another trick to adjusting the float? its 99% there but the accel pump doesn't shoot gas for the first 10-15% of travel which I think is attributed to the gas level in the bowl being slightly too low.

Any suggestions would be great.

 

[Maclin]

The accelerator pump pulls from the bottom of the fuel bowl. I bet the lever is not adjusted properly for the 30cc. I would refit the 50cc.

The proper adjustment for the pump lever is made with throttle wide open. There should be play between the lever and the pump diaphragm button at that point, this is to prevent the lever from travelling too far and hurting the diaphragm or spring inside the pump housing. From idle on up the lever should be touching the diaphragm button with no play.

The squirter nozzles are also part of the pump tuning, and were selected based on the pump shot from a 50cc capacity pump and the actuator cam the lever rides on.

 

[Maclin]

Isn't the sight glass actually a screw in plug? Holley fuel levels in carbs with removeable brass sight plugs are set to where the fuel just wants to run out when the plug is removed. You could revert to this method, or get new clear sight plugs.

 

[tgell001]

I can see embossing theu the paint that indicates level on the side of the bowl similar to the holley 2300s and I assumed there was a sight glass underneath that paint just like the holleys. Don't know why they'd sell me a make and model specific rebuild kit with the wrong accel valve

 

[Maclin]

Probably not the exact kit for that exact Marine model. The kit came with the wrong pump diaphragm for your carb also, right?

 

[keith2k455]

You would rather change the accelerator pump cam instead of adjusting the levers. As previously noted, the cam change will prevent damage to the diaphragm. Using a 30cc to a 50cc may or may not be noticeable. When you quickly increase throttle (from idle or off RPM), you will be looking for what's called a "lean bog" which you can resolve in many different ways - squirters, accelerator pump cams, accelerator pump. Each of these methods for eliminating the bog ( and improving throttle response) has different effects. Easiest route is to leave it the way it was if you were happy with the performance, since performance carb tuning can consume a ton of time and fuel.

 

[tgell001]

I'll probably take it out this weekend and just see if i'm happy with it as is. I know the float level is a tad low because its stumbles a little under subtle acceleration but when given a little more gas enough for the accelerator valve to squirt it jumps up. But its hard to say without being under load if the itll suffer midrange power under WOT with the 30cc pump

 

[Scott Danforth]

the accelerator pump only comes into play when you move the throttle. any RPM range with a steady throttle and the accelerator pump does not even come into the picture.

 

[Maclin]

Regarding this..."I know the float level is a tad low because its stumbles a little under subtle acceleration..." I will re-iterate that the fuel level in the bowl will not be a factor in the accel pump circuit until it is so low that the engine will not run at all, or just barely stay at idle. The squirters should spray out fuel anytime the throttle is moved until about 3/4 throttle. The stumble could be due to a lever adjustment or as mentioned before, the cam on the throttle arm that actuates the accel pump linkage. If you did not remove the cam then I suspect there is play somewhere that needs to be adjusted out, or the WOT play was not set correctly and the diaphragm could have been damaged since the rebuild.

If you removed the cam during rebuild, then this may need to be looked at, as there are 2 mounting holes. One is for normal idling engines, the other has the cam come in later so to speak on racing engines that need the idle set higher.

 

[tgell001]

Im aware. The velocity of the squirt is directly proportional to the velocity of the throttle advance. So if you move the throttle slowly it barely squirts at all

 

[Maclin]

The squirter size controls the duration, and the pump cc volume determines how much fuel is distributed thru the duration, and the cam changes the shape of the duration.