Too high Hydrocarbon on emission tests-Help

[justhorns]

No snake oil, no new cat, just timing... Damn. Ten deg btdc with advance vacuum blocked.

 

[idahovette]

@justhorns that's good about the snake oil...........I hate snakes...............Good outcome tho congrats!!!!

 

[Olegmbuilder]

Quick question. Does this truck have its Evap canister attached? And if so are the tubes clear and connected and the canister cleared from any obstruction? Oh and by the way I live in Colorado and the emissions are getting real strict with the old square bodies that don't have the factory Equipment wont pass. After you check that evap put a new cat on this thing and get its base line settings as close to stock as possible no fiddlefadding with the timing. These old engines are very temperamental with small adjustments .. trust me .. lol

 

[DoubleDingo]

Quick question. Does this truck have its Evap canister attached? And if so are the tubes clear and connected and the canister cleared from any obstruction? Oh and by the way I live in Colorado and the emissions are getting real strict with the old square bodies that don't have the factory Equipment wont pass. After you check that evap put a new cat on this thing and get its base line settings as close to stock as possible no fiddlefadding with the timing. These old engines are very temperamental with small adjustments .. trust me .. lol

It passed. A little late, but still good info

 

[Radiohead]

@justhorns that's good about the snake oil...........I hate snakes...............Good outcome tho congrats!!!!

So that's what is coming out the end of the snake, oil?

And for all that time I thought it was .......something else. Will DEQ fine me for spilling snake oil? lol

 

[justhorns]

Quick question. Does this truck have its Evap canister attached? And if so are the tubes clear and connected and the canister cleared from any obstruction? Oh and by the way I live in Colorado and the emissions are getting real strict with the old square bodies that don't have the factory Equipment wont pass. After you check that evap put a new cat on this thing and get its base line settings as close to stock as possible no fiddlefadding with the timing. These old engines are very temperamental with small adjustments .. trust me .. lol

Still has the evap and its working. They no longer look under the hood or truck (for the cat) They just sniff the exhaust and you either pass or fail.

 

[JBswth]

My great chevy C-10 "ralph" with a 250-6 has just flunked Colorado emissions 8 times. Too High on hydrocarbons (although I have gotten very close to the spec. The Spec is 220 PPM and I have gotten it to 226 on the 6th of 8 tests. They still flunked me after being up at 900! Stinkers.

The engine purrs like a kitten. Spark plugs look good. Truckl runs great. Carb (a Varajet II) has been rebuilt.

I've adjusted mixture with the mixture screw, I've adjusted timing, I've installed all emission equipment that is still functioning. I'm trying not to spend on expensive fixes at this time. Truck is no longer registered due to this issue (expired 7/31/25).

Anyone have ideas?
One option is carb replacement, but, adapter plates are available from the netherlands for a weber, then buy a weber (32/36 dgv), then kludge up a linkage.. air cleaner. I know this varijet II on this truck is a POS, but, its easiest to just tweak what needs tweaking, and cheapest too.

The mixture screw only adjusts idle and low-speed. You might have too high a float - that will result in the low speed and high speed circuits overlapping at a certain throttle position, causing it to be too rich, which will cause you to flunk the HC. Unlike the vehicles of the 60s and older, your's is probably pretty lean, so a slightly over-rich condition will not result in poor performance and/or black exhaust smoke.

J. B.

 

[JBswth]

OK, thanks to all. I set the timing to factory stock settings, and it came in immediately. I have passed emissions and am re-registered for another 5 years! See photo below. Big changes with little effort.

Congratulations for passing!

J. B.

 

[justhorns]

I rebuilt the carb. The float was set to spec. But, the Varajet II is a POS, and I will get rid of it as soon as I can. But, Ralph has the integral head.. Exhaust, intake and the entire head are 1 pc! I have another head of the older style, and am looking for new intake and exhaust manifolds (used is fine), then all I got to do is have the exhaust completely replaced....

 

[AuroraGirl]

My great chevy C-10 "ralph" with a 250-6 has just flunked Colorado emissions 8 times. Too High on hydrocarbons (although I have gotten very close to the spec. The Spec is 220 PPM and I have gotten it to 226 on the 6th of 8 tests. They still flunked me after being up at 900! Stinkers.

The engine purrs like a kitten. Spark plugs look good. Truckl runs great. Carb (a Varajet II) has been rebuilt.

I've adjusted mixture with the mixture screw, I've adjusted timing, I've installed all emission equipment that is still functioning. I'm trying not to spend on expensive fixes at this time. Truck is no longer registered due to this issue (expired 7/31/25).

Anyone have ideas?
One option is carb replacement, but, adapter plates are available from the netherlands for a weber, then buy a weber (32/36 dgv), then kludge up a linkage.. air cleaner. I know this varijet II on this truck is a POS, but, its easiest to just tweak what needs tweaking, and cheapest too.

while waiting in line to test, the cat might cool down, running at a high idle might help

OK, thanks to all. I set the timing to factory stock settings, and it came in immediately. I have passed emissions and am re-registered for another 5 years! See photo below. Big changes with little effort.

oops,nvm, awesome!

 

[AuroraGirl]

I rebuilt the carb. The float was set to spec. But, the Varajet II is a POS, and I will get rid of it as soon as I can. But, Ralph has the integral head.. Exhaust, intake and the entire head are 1 pc! I have another head of the older style, and am looking for new intake and exhaust manifolds (used is fine), then all I got to do is have the exhaust completely replaced....

but youll be down to a 1 barrel, unless you get something aftermarket

Id recommend something that lets you install a rochester 2jet

but realize the varajet ii is complex but its the most versatile 2 barel that allows you to get the most use out of your 250
its a progressive 2 barrel

You must be registered for see images attach

Another source says R45TS for the plug

 

[justhorns]

I'm probably going to go for a Edelbrock 1406 ( 4 bbl) on an offenhauser manifold. Where did you get that chart? Why the dual values for curb idle speed. I'm running r45TS as plugs.

 

[AuroraGirl]

I'm probably going to go for a Edelbrock 1406 ( 4 bbl) on an offenhauser manifold. Where did you get that chart? Why the dual values for curb idle speed. I'm running r45TS as plugs.

if i had to guess, it would be because of the high idle cam of a carburetor

And a 4 barrel 1406 is a LOT of carburetor for a stock 250 inline 6, and it will probably have some touchy driveability

I advise something like a Holly economizer or some other 2 barrel preferably progressive. unless you are getting some mods in that increase air flow a lot

 

[justhorns]

I have a number of customers with 4 barrels on their American 6 cylinders, and they run REALLY well.

 

[DoubleDingo]

I have a number of customers with 4 barrels on their American 6 cylinders, and they run REALLY well.

Have they shared with you any additional information on those 4 barrel holley's? Have they done the Tom Lowe modification where you take a 600 cfm or 750 cfm holley, and modify it to be a 3-barrel? It runs on one barrel and has the two secondaries for get-up-and-go.