Air bubble of doom in gascolator!

[n2582d]

If in fact there is no accelerator pump I'm guessing Jack has an MA-3A carburetor, p/n 10-3103-1,10-4953, or 10-5199, which is used on the Lycoming O-235. The MA-3SPA carburetor for the C-145/O-300 should have a p/n of 10-3237, 10-4439, 10-4895, or 10-4895-1. I don't think having the wrong carb has anything to do with air in the gascolator though.

It would be interesting to tee a plastic tube to the overhead cross-vent line and hook up an airspeed indicator (as a makeshift pressure gauge) to it to see how the pressure/vacuum in the fuel vent line compares with static pressure. Unfortunately Jack isn't flying an experimental aircraft.

I checked fuel flow from both tanks (separately and together) at the input to the carb, and it seemed plenty good, flowed fast a although I didn't actually measure it (gallons/min). I should do that. It flows fast and fine when I just open the valve at the bottom of the gascolator.

The regs call for fuel flow to be 150% of full throttle fuel flow for gravity feed systems. What would that be? Around 15 gph or a gallon every 4 minutes? To rule out obstructions in the fuel lines it might be worth confirming just what you're getting. I'd also do the same check with the fuel valve turned to each tank individually.

[cessna170bdriver]

...I have thought about capping off the primer line but the engine just won't start without a bit of primer, even when warm it need a little. The carb does not have an accelerator pump. (Forgot to get the model number of the carb when I was out there.)...

I wasn't aware that there were ANY C-145/O-300 engines equipped with a carburetor without an accelerator pump...

[4BravoWhiskey]

I checked fuel flow from both tanks (separately and together) at the input to the carb, and it seemed plenty good, flowed fast a although I didn't actually measure it (gallons/min). I should do that. It flows fast and fine when I just open the valve at the bottom of the gascolator.

The regs call for fuel flow to be 150% of full throttle fuel flow for gravity feed systems. What would that be? Around 15 gph or a gallon every 4 minutes? To rule out obstructions in the fuel lines it might be worth confirming just what you're getting. I'd also do the same check with the fuel valve turned to each tank individually.

I did that already, was in another post (getting to be a lot of posts to wade through here!):

I checked flow today. Disconnected line at carb. Kept it as close to normal position as possible.
left only: 33.0 gph
right only: 33.0 gph
both tanks: 41.8 gph

I think there is no venting issue and no flow restriction with those rates. I checked the fuel hoses and they look totally smooth and clear. Collected about 8 gal and didn't see any new air accumulation in gascolator.

Repeated with tail raised. flow rates increased by about 2 gph. that was the only change.

[canav8]

4bravowhiskey, there has been so many posts on this thread by members of this association. We are all friends and respected forum participants. There has been a lot of good advice given to you, Im curious, are you a member of this organization currently? You are missing the TICA 170 logo above your name. Doug

[4BravoWhiskey]

I am. I was in '99-'06 when I had my previous 170, and then again starting just about two years ago when I bought another. I moved earlier this year and didn't get my notice that membership was due, but just paid that when I realized it. Is there anything else you would like to know?

[canav8]

I am. I was in '99-'06 when I had my previous 170, and then again starting just about two years ago when I bought another. I moved earlier this year and didn't get my notice that membership was due, but just paid that when I realized it. Is there anything else you would like to know?

Excellent, you should get a hold of Bruce to rattle the Sabre and get them to put an icon up there for you on the website forum that way more members would be inclined to help you. That image is what tells if you are a TICA170 member and not just a forum poster if you didnt know that. Kindest. Doug

edited: That was fast.

[4BravoWhiskey]

Ha, really fast! In fact your inquiry led me to check into it again, and I discovered that my Paypal transaction didn't go through (long story) so I re-sent it. I appreciate your pointing this out! This is a fantastic association and very happy to support it.

[c170b53]

And we are extremely happy to have members such as yourself presenting puzzles better than the NY times weekend crossword !

[blueldr]

My curiousity has made me review this thread from the start again. My conclusions are:

The initial problem occurred following a relatively long flying period since the last inspection. It required a full rich mixture to accomplish a rough running engine to reach a landing area.
These very same symptoms occurred with my airplane when it had the O-300 engine and I had more than a hundred hours on it during a flying summer. It was very late in the day, and I managed to drag it into Baker, Oregon, and spent the night there. The next morning everything checked OK on the run up so I headed on to Bend, oregon. After about an hour of flying, it developed the same symptoms. Again the next morning, in Bend, everything checked just fine so I headed on home to California. Same symptoms again. I made it home and stuffed it in the hangar. The next day I pulled the cowling to start a 100 hr. and the first thing I did was to pull the spark plugs.
They were completely clogged up with lead crud! I had been running a lot of short flights on 100LL all summer up in Idaho where no mogas was available. I was used to using unleaded mogas at home and the spark plugs just never needed any cleaning.
A set of cleaned up spark plugs completely alleviated the problem that I had assumed was a fuel thing.

Incidentally,did we ever determine if this airplane witout an accellerator pump has a legal carburetor by part number ???

[4BravoWhiskey]

Thanks for going to the effort to review the whole thing again, blueldr!

I was out there yesterday and checked several spark plugs and they all looked fine. And I have not had any reoccurrence of rough engine since that day in Utah.

I took the cowl off and lo and behold, my carb DOES have an accelerator pump.

Very sorry about this confusion. I had looked at the wrong side of the carb, thinking it was supposed to be where the throttle linkage connects (that's how it was on the example my mechanic had shown me). And the cowl was on and it was hard to see up in there. The carb is part no. 10-3237. I missed seeing the model no., I took a photo but it's blocked by the engine mount.

So, I made a new effort to start the engine without primer and I was successful with the engine warm, although I do think the accelerator pump might need an overhaul. But anyway, this is clearly not the main issue.

I did not have time to plug up the primer connection on the gascolator and try it out (on the ground!) but I now have the required plug and I'm set to try that next time.

[MoonlightVFR]

48Whiskey


I am so so relieved.

You do indeed have an accelerator pump!

I am sure that you know ourr carb was original for a farm tractor and sold retail for 4.50 each.. But that is just history.

Time to time check the external mechanical linkage on carb for binding. Simple lube is sometimes overlooked. Costly!
It happens.

Is there a picture of your bubble i can view?

[4BravoWhiskey]

I guess the less complicated the carb the better. The throttle operates smoothly, there is no binding or anything in the linkage.

The best picture I have is this one. Note that the engine was running perfectly fine with this air bubble. It has been larger than this at times.

(For some reason the preview is showing the image sideways, but when I click on it, the picture is oriented correctly.)

[n2582d]

Is it possible that the gascolator is mounted / hooked up backwards? There is an "In" port, and an "Out" port. I have heard of cases with symptoms like yours which resulted from just such a reversal.

I don't have a picture of the gascolator handy but will take one next time I'm out there. The input and the pickup are both at the top, as is the primer connection. The input has a stand pipe going down through the filter, so it is always lower than the air bubble. The output (pickup) is just a hole in the top assembly, no pipe coming down. This is how my mechanic said it should be. Does this sound correct? I can't tell from looking at the 100 series service manual.

It sounds to me like you have it installed correctly but, in looking at the IPC, there should be an "IN" and "OUT" marked on the top of the respective ports. Grasping at straws here but might be worth double checking.

[4BravoWhiskey]

It sounds to me like you have it installed correctly but, in looking at the IPC, there should be an "IN" and "OUT" marked on the top of the respective ports. Grasping at straws here but might be worth double checking.

According to the diagram it is installed correctly, because the primer line is on the correct side.

[blueldr]

Oh !! It really does have an accellerator pump ?? OK, I guess I'll just throw in the towel on this whole thread.