Its a bit early to tell for sure since I did the swap over winter and I'm just getting it back on the road. Last fall I determined that the throttle shafts were worn on the HS6s. I was having trouble tuning it. I would get it about right and then it acted like it wasn't tuned again. It was hard to keep a consistent idle and lacked power.

I located a pair of HIF6s from an early '70s 140 series with the square air box which solved the issue of the expensive round filters on the HS6s. I rebuilt the HIF6s while they were off. In the process I wanted to replace the manifold gasket. I pulled it and found out the manifold had a crack and it looked like someone had tried to repair it. I found a nice replacement. I changed the manifold and exhaust studs in the process.

So far all the issues I had are gone and its running well. Idle is good and it seems to be staying tuned now. Power is consistent and it feels like it is running like it should. Its a B18 and the paperwork I got with the car shows it was rebuilt not long before I got it. Compression tests appear to confirm this.

My feeling is if you have a good set of HS6s you would not notice anything swapping. For performance I think a good set of HS6s. For drivibilty the HIF6 might have the edge. My opinion. The HIF6 start to show signs of emissions coming into play with the hot start devices being added.

The two noted differences I see are the cold start enrichment and integrated float bowl. The cold start is only on one HIF6. Seems like a better design over the choke setup on the HS6. Time with tell on that. The integrated float bowl eliminates the fuel tube going from the float bowl on the HS6 to the carb. The lid on the HIF6 float bowl is facing down so hopefully that seal holds up well.

I could have just had bushing put in the HS6s but I wanted to give the HIF6s a try. It was suggested the HIF6s might run a bit rich on the B18 and I will keep an eye on the plugs for that. I think it has BBB needles. The HS6 might have a broader selection of needles. So it appears I had two issues. Worn throttle shaft bushings and a cracked combo manifold.

I can update as I drive it more. I do have a '75 electronic dizzy to put in once I confirm all is well with the carbs. I also have a GT cluster to install as well but might face tach issue with the dizzy. Last summer I pulled the BW35 and installed a M41 with overdrive. I also changed the rear axle seals and fluid. The summer prior I rebuilt the front end with bushing and ball joints and changed the seals on the steering box. It slowly coming together. Its no 142 but the '68 144 was looking for a home and I took it in. The body is in excellent shape. Paint is a bit faded and I might address that in years to come.

Things went smoother and correct by being able to crowd source this board for answers. Thanks to all!

Craig