2.4L Chrome 175 "Funny" Sound

[croSSed]

I have a rebuilt 175 - new pistons, rings, rods, 15 over steel sleeve in #1. It's just broken in. I put one size bigger main jets in the carbs just to be safe. It is a drop-on powerhead that is replacing a 2L XR2 150 (which runs great), I just wanted the extra torque. The extra top speed is just a bonus. This 175 runs great at high throttle positions, but at slower cruising speeds it runs kind of "ratty." It has a harmonic sound coming from it, kind of like one hole is firing differently than the others, or it also kind of sounds like bearing noise. Not loud and alarming, just not "right." My 150 does not make this sound. It also doesn't run very smoothly at displacement speeds, compared to my 150. Carbs were gone through, new floats, set float height, new needles, they look really good. Any ideas what this could be? I don't want to just start changing parts w/o some idea of where to start. TIA!

[paradak]

I am not an expert by any means. I have rebuilt my 175 (1985 chrome bore) recently. I do not have any funny sounds. Hopefully you used Locktite Red on the rod bolts and made sure the rod caps were aligned properly to the rods. If that was all good then I would suspect carburetion or sync & Link and timing settings. I had an issue where after rebuilding the carbs, the float bar screw was loose and flooded one cylinder. This was my bad but the motor ran pretty good in that condition till I diagnosed it. Just a thought. Runs better now of course.

[ctobias1984]

Not sure you're going to notice any top speed difference between a normal 175 and a hot 150. They both basically make the same HP at the prop.

[tlwjkw]

Not sure you're going to notice any top speed difference between a normal 175 and a hot 150. They both basically make the same HP at the prop.

gotta disagree with ya on this.. a "good" 175 will, in a lotta cases, run with a 200.. it uses tha same chrome bore block as a 200.. different front half.. a strong one usually makes something jus north of tha 175 hp........ jmo

[pcrussell50]

gotta disagree with ya on this.. a "good" 175 will, in a lotta cases, run with a 200.. it uses tha same chrome bore block as a 200.. different front half.. a strong one usually makes something jus north of tha 175 hp........ jmo

This is what I would expect, too.

I have a 2.4/200 and a 2.0/150. And run them on the same boat. The extra displacement of a 2.4/200 over a 2.0/150 can be felt.

I don't have a 2.4/175, But I'd bet that the extra 25 hp that a 2.4/200 holds over a 2.4/175 is mostly felt at the very top end, (where I rarely go in my recreational usage). In fact I wonder if the 2.4/175 might be torquier than the 2.4/200?

-Peter

[ctobias1984]

gotta disagree with ya on this.. a "good" 175 will, in a lotta cases, run with a 200.. it uses tha same chrome bore block as a 200.. different front half.. a strong one usually makes something jus north of tha 175 hp........ jmo

hmm interesting.. I always read that the xr's made right around 170 at the prop and assumed a 175 would as well.

[tlwjkw]

XR is just mainly a merchandising badge.. they do have a coupla things (carburetor's, tuner two main things) that spice it up a little but not much.... lotsa stories out there................. jmo.

[ctobias1984]

XR is just mainly a merchandising badge.. they do have a coupla things (carburetor's, tuner two main things) that spice it up a little but not much.... lotsa stories out there................. jmo.

And a faster lower unit which helps top speed

[tlwjkw]

yeah, forgot about that for some reason cause thats all i ran (XR6) on my hot rods back in tha day.......

[skialot2]

XR is just mainly a merchandising badge.. they do have a coupla things (carburetor's, tuner two main things) that spice it up a little but not much.... lotsa stories out there................. jmo.

There is a big difference between a regular 150 and an XR150. There is the different carbs and tuner. They use a different throttle cam. They have the small bullet lower unit with a 1.87 ratio instead of a 2 to 1 ratio. But the biggest difference is the XR150 uses a 2.4 liter block like the 175 and 200. not a 2.0 liter. They have a little more horsepower than a regular 150. But they have a lot more low end torque.

[pcrussell50]

There is a big difference between a regular 150 and an XR150. There is the different carbs and tuner. They use a different throttle cam. They have the small bullet lower unit with a 1.87 ratio instead of a 2 to 1 ratio. But the biggest difference is the XR150 uses a 2.4 liter block like the 175 and 200. not a 2.0 liter. They have a little more horsepower than a regular 150. But they have a lot more low end torque.

When you say “XR150”, do you mean the 150XR2?

I have a couple of 150’s from the 2.0/2.4 era. And one of them is an XR2, based on its serial number on the block.

-Peter

[tlwjkw]

Lesson for tha day.............

He only has half a clue.. first there are 3 different XR series motors.. true all tha XR series are 150's but all different.. first XR2 150 was 2.0 motor.. it had different carbs and tuner from tha "production 135/150 but uses same rotating assy... ALL 2.0 motors had standard gear case with 2 ta 1's.. tha XR4 is a 2.4 with tha small gear case with 1.78's (only production gears that fit tha small case).. its a not a chrome bore like tha 175/200.. tha 4 is the one and only "steel sleeve" (not chrome which makes tha 175/200 what they are) 2.4 merc ever made.. tha porting is no where close to tha 175/200.. they are notorious for tha sleeves being "turned" a scosh and not lined up with tha block porting.. no one knows (if they do they're not sayin') for sure if this is done intentionally or justa manufacturing flaw.. the small gear case had 1.78's and nothing else... 2 ta 1's were standard on tha 2.0 motor and 1.87's on everything else EXCEPT tha small case (XR4/XR6) which is tha 1.78's... XR6 (2.5) completely different from all tha rest.. small gearcase (1.78's) for first few years (why they got scarce in tha hot rod world) then went to tha regular case with mostly 1.87's...... a guy named Steckbauer machined tha 2 ta 1 stuff ta fit tha small case along with some other mods ta make 'em strong enough ta take a lot of HP... they are affectionally known as stecky's... most were non-shiftable... those cases are really hard ta come by now.. don't think anyone else is doin' it anymore although i think someone is or was makin' a billet carrier for it.....

there all kinds a stories 'bout tha XR series motors as for them being "something special" jus gets exaggerated in my opinion.. they do perform a little better than tha "factory" motors mostly but not by much...... but there's nothin' ta compare tha XR4 to since its tha only steel sleeve 2.4 they ever built!

[ctobias1984]

So maybe an xr2 would be a different story but I dont think I would notice any speed difference going from my xr4 to a 2.4 175

[tlwjkw]

if you don't then ya have something amiss somewhere.............. a healthy 2.4 175 will run really close to tha 200....... jus cause its a "2.4" they are completely different..

[skialot2]

When you say “XR150”, do you mean the 150XR2?

I have a couple of 150’s from the 2.0/2.4 era. And one of them is an XR2, based on its serial number on the block.

-Peter

No, not the XR2/Magnum. that is a 2.0 liter. But the XR4/Magnum II, and the early XR6/Magnum III are all 2.4 liter engines. the later XR6/Magnum III is a 2.5