Trollhole Carb - Secondary Not Opening

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

roadstr6

roadstr6

10 Year
Joined
Apr 10, 2013
Threads
90
Messages
5,829
Location
Weddington, NC
Guys,

I have an old Trollhole carb on my 40 that was rebuilt several years ago. I've been running it for a couple of years. I decided to get everything in a good state of tune last night and discovered that the secondary isn't opening. Apparently it never has ( at least not in the last couple of years)! I did the paper clip trick to test and it didn't move. The mechanical linkage will open it that first little bit but the vacuum never takes over and opens it all the way. I pulled the vacuum diaphragm and checked it (good) and even swapped the diaphragm for one on a brand new Trollhole carb that was on the shelf (NIB). Still, no movement. I removed the diaphragm and blew carb cleaner into the orifice on the carb. Followed the carb cleaner with a shot of air from my compressor. The air came out as a light mist in the primary, just as I would have expected it to do. The secondary shaft is not binding and moves freely when cycled by hand. Any ideas? I sure could use the extra "oomph" that the secondary is supposed to supply. My truck struggles to pull up long mountain hills. Around town it does just fine. In fact, after tuning it last night it runs the best it has in years but I want more!

Dave
 
Is there a mechanical blockage that occurs when the carb is bolted down to the manifold? I have seen this a few times, often it happens when the hole in the manifold is smaller than the hole in the carb. This usually allows the butterfly to open a little ways, but it won't open all the way.
 
I don't think so. I can operate the secondary butterfly through a full range of motion by hand once I cycle the primary linkage to allow it to crack open that first little bit. Carb is installed in the truck. Nothing interfering.
 
You need to increase the mechanical opening of the secondary by bending the tab that kicks it open. There needs to be vacuum in both barrels for the secondary actuator to function and the secondary only gets vacuum when it is open. Also make sure that the linkage opens the primary throttle all the way or the secondary will never kick in.
 
I will try bending the tab and see how it does. I will also verify that the primary is getting WOT. The secondary already opens a tad via the mech linkage, but maybe just not far enough to get the vacuum started. Thanks for the advice, PH. I'll report my findings. I feel somewhat silly even messing with it given that I have another brand new carb in a box but this one has been fine for several years with the exception of the inop secondary. I'd like to save the new carb for my 60 once I de-smog it.
 
Last night I lengthened the vertical rod on my accelerator linkage by about six threads to provide a little more push and finally got the secondary to open at WOT. I confirmed this via the paper clip trick. The linkage seems to be pretty worn with too much slop in the ball and sockets and also there is quite a bit of movement in the rubber grommet in the bracket on the firewall. Anybody know any cheap fixes for this? Truck ran like a raped ape but after a short drive the carb began to stumble unless I really put my foot in it. When I got home I decided to pull the fuel line off the front of the carb and low and behold there was some debris in the inlet screen. I tried to use a magnet to pull it out but it was not metallic. It looks like some tiny shreds of FIPG. I decided that rather than pull the carb top off while on the engine, I'd just yank the carb and clean it. While I had it off I made the decision to go ahead and swap in the NIB Trollhole carb I had on the shelf. Swapped the carb on, set everything and drove the truck around for a while. It drove great BUT the secondary never kicked in. UGH! Looks like I need to come up with a fix for the sloppy linkage issue and maybe bend the tab that opens the secondary on this new carb. Once I open up the old carb and clean it I will shelve it for my next project. Any homebrew ideas on how to freshen up the sloppy linkage would be appreciated!
 
FWIW - One of my PO's decided to use a small section of fuel line for the accelerator torque rod linkage grommet, 90480-15227 that must have been worn out. This improvised part may have worked for a short period of time, but was worn out and caused my linkage to not function properly. I order the OEM $4 grommet, installed it, and the linkage works like Mr. Toyoda intended it too.

This is the 78107A grommet in the photo below.
MB4977I.png
 
Ordered the grommet from the local Toyota stealership. $9.00 and it will be in tomorrow. Beats ordering from SOR. Still, $9 is highway robbery!
 
GA Architect said:
FWIW - One of my PO's decided to use a small section of fuel line for the accelerator torque rod linkage grommet, 90480-15227 that must have been worn out. This improvised part may have worked for a short period of time, but was worn out and caused my linkage to not function properly. I order the OEM $4 grommet, installed it, and the linkage works like Mr. Toyoda intended it too.

This is the 78107A grommet in the photo below.
Click to expand...

Good to know Rick - thanks for sharing!
 
I give up. Replaced the firewall grommet. Bent the secondary tab. Verified throttle kicks the secondary butterfly open. Can operate secondary by hand. Diaphragm is good. Still no secondary action. Paper clip moves down about 3/8" just from the mechanical action. Vacuum does not take over. Carb has been on and off four times now with me dicking around with it. This sucks. I'm done. Truck runs good enough. Screw it.
 
Okay. I gave it one last try and had to resort to drastic measures to get this thing working right. Here's what I did: The idea is to bend this little tab to open the secondary more than the original setup.
image.webp

The problem is that if you bend it too far the secondary will stay cracked open even at zero throttle. Not an ideal situation.

I decided to do a little grinding on the cam blade that contacts the tab to provide additional clearance at zero and part throttle while allowing me to further bend the tab to allow the secondary to open a tad more.
image.webp


Here I have shaded the cam blade to show the material I ground away.
image.webp


Here are before / after shots of the secondary butterfly at WOT before and after my mod. Before the mod it opened 3/32". After 11/64".
image.webp
image.webp


I reinstalled the carb and verified that the secondary is now working properly.

This mod clearly helped in my situation. I will say this in closing: I have 4:10 (factory) gears and 35" tires. I believe part of my issue with the secondary is the fact that in 4th gear, I never hit the revs necessary to create a big vacuum. My speedo reads 10-12 mph slower than my actual speed. If the secondary is supposed to open at 40-50mph with factory wheels and tires, I've got to run 50-60mph in 4th gear to build the vacuum necessary to open the secondary. At that speed it's just not really needed. I don't run this rig at 75-80 mph. I think the only time the secondary will truly be in use is in a hard pull in 3rd gear.
 
Last edited:
Update: The truck runs great down the road but I have a new problem. It is idling really rich. Exhaust smells strong of unburned fuel and is really dark. Sitting in one spot for a few minutes it will leave a black spot on the driveway where the exhaust is blowing down from the tailpipe. If I disconnect the idle fuel solenoid it leans out a tad and the gas stink goes away for the most part. It does continue to run (better actually) with the idle fuel solenoid disconnected. It is obviously getting fuel from some place other than the IFS at idle. This is true even when I turn the idle speed screw down until it is barely running. I have the idle mixture screw pretty lean (1-1/2 turns out). The fuel level is in the middle of the sight glass so I don't believe it is flooding but it is getting idle fuel outside of the IFS. Wonder what the issue could be? BTW, this is a brand spanking new Trollhole carb. Anybody able to offer assistance? @Trollhole or @pinhead?
 
If your engine still runs with the idle solenoid disconnected then you're getting fuel from something other than the idle circuit.
Given the messing around that you've done with the secondary....is it possible that the secondary is open at idle now?
That's the first thing I'd check. That seems most likely.
If it's not that, it's really common when people have a big vacuum leak or something else that causes their engine not to idle, to crank down on the idle speed screw until it idles ok. If you overdo this, it opens the throttle exposing the transition slot or even further. Now your idle fuel is not coming from the idle circuit-with the symptom that the idle mixture screw doesn't affect the idle like it should and the idle solenoid doesn't shut down the engine at idle.
 
Send the carb to me and I'll take care of you.

Your secondary is open at idle making the motor run rich.
 
Okay guys! Thanks for the input. I'll check the function of the secondary. Marshall, I'll try to troubleshoot it myself before I send it to you. If you read through this thread you will see that I monkeyed around with the secondary quite a bit because initially I couldn't get it to open at all. I may have bent the tab up too far, causing it to stay cracked open a little. I'll check it and report back.
 
Thanks again for the responses guys. I got it sorted out tonight. In my tweaking of the secondary butterfly tab I had bent it up just a hair too much leaving it cracked open. I bent the tab back down, hooked up the idle fuel solenoid and re-set the idle speed screw and mixture. Truck idles good now and no sooty exhaust.
 
That makes sense. The ultimate test is: Does it stall out when you disconnect the solenoid wire and does it stall out as you bottom out the idle mixture screw?

Kudos to trollhole for standing behind his product.
 
To answer the test questions, yes and yes. Oh, and I totally agree about Marshall standing behind his product. Thanks man! The truck runs the best it ever has with this new carb. Woohooo!
 
You must log in or register to reply here.

Share this page

Back
Top Bottom